Systems and methods for water extraction control

ABSTRACT

A controller may control a system for extracting liquid water from air comprising a thermal unit, a primary desiccant wheel, and a regeneration fluid path. The controller may comprise a plurality of sensors, a plurality of motors, and a microcontroller coupled to the plurality of sensors and the plurality of motors. The microcontroller may be configured to determine a water extraction efficiency based on at least one signal received from at least one of the plurality of sensors and maximize the water extraction efficiency by adjusting a speed of at least one of the plurality of motors in response to the determined water extraction efficiency. The water extraction efficiency may be a value obtained by multiplying a regeneration fluid flow rate within the regeneration fluid path by an absolute humidity of air on a side of the primary desiccant wheel opposite a side in communication with the thermal unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/339,649, entitled “Systems and Methods for Water Extraction Control”and filed May 20, 2016, by reference in its entirety.

This application incorporates U.S. Provisional Application No.62/145,995, entitled “Systems and Methods for Generating Liquid WaterFrom Air” and filed Apr. 10, 2015, by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system for generating liquid water from airaccording to an embodiment of the invention.

FIG. 2 is a diagram of a system for generating liquid water from airaccording to an embodiment of the invention.

FIG. 3A is a graph of diurnal variations in environmental conditionsover one day, including ambient air relative humidity (“RH”) andtemperature, according to an embodiment of the invention.

FIG. 3B is a graph of diurnal variations in environmental conditionsover one day, including solar radiation (e.g., solar insolation),according to an embodiment of the invention.

FIG. 4 is a diagram illustrating flow paths through systems forgenerating liquid water from air according to an embodiment of theinvention.

FIG. 5A is a diagram of a controller according to an embodiment of theinvention.

FIG. 5B is a diagram of a control process according to an embodiment ofthe invention.

FIG. 6 is an efficiency graph according to an embodiment of theinvention.

FIGS. 7A-7F show a series of efficiency graphs according to anembodiment of the invention.

FIGS. 8A-8F show a series of water production rate graphs according toan embodiment of the invention.

FIGS. 9A-9F show a series of water production rate graphs according toan embodiment of the invention.

FIG. 10 is an efficiency graph according to an embodiment of theinvention.

FIGS. 11A and 11B are graphs illustrating coefficients of quadraticregression models fit to the data sets illustrated in FIG. 10 accordingto an embodiment of the invention.

FIG. 12 is a diagram of a system for generating liquid water from airaccording to an embodiment of the invention.

FIG. 13 is a diagram of a controller according to an embodiment of theinvention.

FIG. 14 is a go/no-go mode determination process according to anembodiment of the invention.

FIG. 15 is a network of water generating systems according to anembodiment of the invention.

FIG. 16 is a diagram of a maximum power point tracking approachaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

The systems and methods described herein are generally related tocontrol systems for the extraction of water vapor from atmospheric air.First, a general description of water extraction by a water extractionsystem is provided. Then, specific control system embodiments arepresented in the context of specific water generation system examples.

Water Extraction

Referring now to the drawings, and more particularly to FIG. 1, showntherein and designated by the reference numeral 10 is an example systemfor generating liquid water from air. System 10 may be configured tofunction responsive to diurnal variations. For example, as described inmore detail below, system 10 may be configured to control one or moreoperational parameters (e.g., control and/or controlled variables) basedon one or more diurnal variations (e.g., variations in ambient airtemperature, ambient air relative humidity, solar insolation, and/or thelike).

System 10 may comprise a desiccant unit 14. Desiccant unit 14 maycomprise a desiccant (e.g., sorption medium) 18, where the desiccant 18(e.g., or a portion thereof) may be selectively (e.g., and/oralternatively) movable between an adsorption zone 22, in which thedesiccant is in fluid communication with a process air pathway (e.g., aprocess airflow path) 26 and a desorption zone 30, in which thedesiccant is in fluid communication with a (e.g., closed-loop)regeneration fluid pathway (e.g., a regeneration fluid path) 34. In someembodiments, the adsorption and desorption zones may be defined by ahousing (e.g., 38) of the desiccant unit.

Desiccant unit 14 may operate in a continuous, or non-batch, fashion,such that desiccant unit 14 is configured to absorb water and desorbwater substantially simultaneously or simultaneously. For example,system 10 may be configured such that a first portion of desiccant 18can be disposed within adsorption zone 22 (e.g., such that the firstportion can capture water from process air in process air pathway 26),with a second portion of the desiccant simultaneously disposed withinthe desorption zone (e.g., such that the second portion can desorb waterinto regeneration fluid in regeneration fluid pathway 34). Regenerationfluids suitable for use in some embodiments of the present systems mayinclude, but are not limited to, air (e.g., including any suitableamount of water vapor), super-saturated or high relative humidity gas(e.g., 90-100% relative humidity), glycols, ionic liquids, and/or thelike.

Desiccant unit 14 may comprise a hygroscopic material (e.g., desiccantor sorption medium 18) configured to continuously alternate between aprocess air pathway 26 and a regeneration fluid pathway 34. In someembodiments, that the desiccant or sorption medium may be capable ofquickly desorbing water back into low relative humidity air (e.g., toregenerate the desiccant). Therefore, in some embodiments, theperformance of the desiccant or sorption medium may be driven by anability to quickly cycle through an absorption state and a desorptionstate.

Desiccants 18 may comprise any suitable medium in any suitableconfiguration (e.g., such that the desiccant or sorption medium iscapable of adsorption and desorption of water). In some embodiments, thedesiccant or sorption medium may be capable of sorption at a firsttemperature and/or pressure and desorption at a second temperatureand/or pressure. Suitable desiccants or sorption mediums may compriseliquids, solids, and/or combinations thereof. In some embodiments,desiccants or sorption mediums may comprise any suitable porous solidimpregnated with hygroscopic materials. For example, desiccant 18 maycomprise silica, silica gel, alumina, alumina gel, montmorillonite clay,zeolites, molecular sieves, activated carbon, metal oxides, lithiumsalts, calcium salts, potassium salts, sodium salts, magnesium salts,phosphoric salts, organic salts, metal salts, glycerin, glycols,hydrophilic polymers, polyols, polypropylene fibers, cellulosic fibers,derivatives thereof, and combinations of thereof. In some embodiments,the desiccant or sorption medium may be selected and/or configured toavoid sorption of certain molecules (e.g., molecules that may bepoisonous when consumed by a human).

In some embodiments, desiccant particles may be packed in a shallow bedto maximize a surface area for interaction with air or fluid withinadsorption zone 22 and desorption zone 30. In some embodiments, thedesiccant particles may be agglomerated via a binder. In someembodiments, the desiccant particles may be dyed black (e.g., to improveabsorption of thermal radiation). In some embodiments, the desiccantparticles may be mixed and/or combined with thermal radiation absorbingmaterials.

System 10 may include one or more blowers 42 and/or one or morecirculators 46. For example, in this embodiment, blower 42 is disposedin process air pathway 26 and is configured to adjust a flow rate of airthrough the process air pathway. Circulator 46, in this embodiment, isdisposed in regeneration fluid pathway 34 and is configured to adjust aflow rate of fluid through the regeneration fluid pathway. In someembodiments, blower 42 and/or circulator 46 may be controlled bycontroller 50 (e.g., controlling a speed of blower 42 and/or circulator46 to optimize liquid water production). In some embodiments, blower 42and/or circulator 46 may be configured to substantially maintain apre-determined flow rate through process air pathway 26 and/orregeneration fluid pathway 34, respectively.

System 10 may comprise a thermal unit 54 configured to provide thermalenergy to fluid in regeneration fluid pathway 34 (e.g., such thatdesiccant 18 may be regenerated). In some embodiments, thermal unit 54may be a solar thermal unit (e.g., is configured to convert solarinsolation to thermal energy). While the present systems may compriseany suitable thermal unit, whether solar or otherwise, the followingdescription of thermal unit 54 is provided by way of example.

Thermal unit 54 may comprise a transparent layer 62 configured to allowsunlight to enter casing 58 of the thermal unit (e.g., a sheet oftransparent material, a lens, and/or the like, which may comprise glass,polymers, polycrystalline materials, derivatives thereof, combinationsthereof, and/or the like). In embodiments comprising a glass transparentlayer 62, the glass may be configured to maximize transmissivity (e.g.,low-iron and/or no-iron materials, and/or other compositions, uncoatedmaterials, and/or the like). Transparent layers may comprise multiplelayers (e.g., multi-pane layers, such as, for example, double-panedglass).

Thermal unit 54 may comprise an absorber 68 configured to absorb thermalenergy from the sunlight and provide at least a portion of the absorbedthermal energy to fluid in the regeneration fluid pathway (e.g.,absorber 68 may comprise a thermally permeable material). Absorbers maycomprise any suitable material, such as, for example, metals (e.g.aluminum, copper, steel), thermally stable polymers, or other material,and/or the like. Absorbers may be substantially flat, roughened,channeled, or corrugated, for example. In some embodiments, a matteblack coating or selective film may be applied to the surface of theabsorber material. Absorber 68 may be configured to transfer thermalenergy to fluid in the regeneration fluid pathway without an interveningheat transfer fluid in some embodiments. In other embodiments, a fluid(e.g., liquid, gas, and/or the like) may be thermally disposed betweenthe absorber and fluid in the regeneration fluid pathway (e.g., tofunction as a medium to transfer heat between the absorber and fluid inthe regeneration fluid pathway).

Thermal unit 54 may comprise an insulator 72 configured to insulate atleast a portion of casing 58. In this way, solar insolation may enterthe casing of thermal unit 54 (e.g., through transparent layer 62), andinsulator 72 may insulate a portion of the casing to, for example,minimize thermal energy losses to an environment outside of the thermalunit. Insulator(s) may comprise any suitable material (e.g., a materialcapable of resisting the flow of thermal energy), such as, for example,a solid foam comprising trapped pockets of gas and/or liquid. In someembodiments, insulators may be selected and/or configured for stabilityat high temperatures (e.g., temperatures exceeding 200° C.).

One or more channels 76 may be disposed in thermal communication withabsorber 68 such that the absorber may transfer absorbed thermal energyto fluid (e.g., regeneration fluid, a flowable heat carrier medium,and/or the like) within the one or more channels. The one or morechannels 76 may form part of regeneration fluid pathway 34 (e.g., one ormore channels 76 are configured to convey regeneration fluid). The oneor more channels 76 may comprise any suitable structure, such as, forexample, tubular hollow bodies or a plurality of flat plates adapted forfluid flow therebetween, and/or the like.

System 10 may comprise a condenser 80 configured to receive fluid fromthe desorption zone via the regeneration fluid pathway and produceliquid water from the received fluid (e.g., by condensing water vapor influid in the regeneration fluid pathway). Condensers may comprise anysuitable material and may be of any suitable configuration (e.g., tocondense water vapor in regeneration fluid into liquid water). Forexample, suitable condensers may comprise polymers, metals, and/or thelike. Condensers may be arranged to include coils, fins, plates,tortuous passages, and/or the like. Condenser 80 may be configured totransfer thermal energy from fluid in regeneration fluid pathway 34downstream of desiccant 18 to air in process air pathway 26 upstream ofdesiccant 18 (e.g., such that air in process air pathway 26 mayfacilitate cooling of condenser 80). In some embodiments, condenser 80may be cooled by ambient air.

System 10 may comprise a water collection unit 84 configured to receiveliquid water produced by condenser 80. Liquid water produced by thecondenser may be provided to water collection unit 84 by way of gravity;however, in other embodiments, flow of liquid water from the condenserto the water collection unit may be assisted (e.g., by one or morepumps, any other suitable delivery mechanism, and/or the like).

System 10 may comprise a filter 88 (e.g., a filtration membrane), whichmay be positioned between condenser 80 and water collection unit 84(e.g., to reduce an amount of impurities, such as, for example, sand,bacteria, fibrous, carbonaceous species, and/or the like, which may bepresent in liquid water produced by condenser 80).

Water collection unit 84 (e.g., or filter 88 thereof) may comprise anultraviolet (UV) light source (e.g., for disinfection of water producedby condenser 80). In some embodiments, suitable light sources maycomprise light emitting diodes (LEDs) having, for example: wavelengthsbelow 400 nanometers (nm) (e.g., 385 nm, 365 nm, and/or the like),wavelengths below 300 nm (e.g., 265 nm), and/or the like.

Water collection unit 84 may comprise one or more water level sensors(e.g., 122 e). Such water level sensors may comprise conductance sensors(e.g., open and/or closed circuit resistance-type conductance sensors),which may operate via conductivity measurement of water in the range of0.1 msiemens per cm.

Water collection unit 84 may comprise a receptacle 92 configured toreceive one or more additives for introduction to the produced liquidwater. Such additives may be configured to dissolve slowly into liquidwater stored in the water collection unit. Additives may include, butare not limited to, minerals, salts, other compounds, and/or the like.In some embodiments, additives may impart flavor to the produced liquidwater. For example, additives may include potassium salts, magnesiumsalts, calcium salts, fluoride salts, carbonate salts, iron salts,chloride salts, silica, limestone, and/or combinations thereof.

System 10 may comprise indicators (e.g., lights, such as, for example,LEDs), which may be configured to provide information regarding systemoperation. For example, in some embodiments, indicator lights may beconfigured to provide information (e.g., visually, for example, to auser) that the system is running, that solar power (e.g., from powerunit 118) is available, that an air filter (e.g., within process airpathway 26) may need to be changed, that a water collection unit (e.g.,84) is full (e.g., in some embodiments, that the water collection unitcontains 20 L of liquid water), that an actuator (e.g., actuator 114,blower 42, circulator 46, and/or the like) has failed and/or is failing,that telematics errors (e.g., as indicated by transceiver 126 operation)have and/or are occurring, and/or the like. As described below, anysuitable information (including the information described above withreference to indicators) may be transmitted over a communicationsnetwork (e.g., alone and/or in addition to operation of any indicators).

A controller (e.g., processor) 50 may control exposure of desiccant 18(or a portion thereof) to air in process air pathway 26 and regenerationfluid in regeneration fluid pathway 34 (e.g., to increase and/oroptimize the liquid water ultimately produced by condenser 80), and suchcontrol may vary over a diurnal cycle (e.g., in response to diurnalvariations). Such variations in environmental conditions (e.g., inputsinto controller 50) may include, for example, ambient air temperature,ambient air relative humidity, and solar insolation. Other inputs tocontroller 50 may include, for example, an amount of thermal energygenerated by thermal unit 54, a relative humidity of air in process airpathway 26, a relative humidity of fluid in regeneration fluid pathway34, a temperature of fluid in the regeneration fluid pathway betweendesiccant 18 and thermal unit 54, a rate of water production, and/or thelike. In embodiments that include a purge airflow path (e.g., 130),inputs to controller 50 may include a flow rate, temperature, relativehumidity and/or the like of air in the purge airflow path. Controller 50may be configured to optimize liquid water production by controlling arate of desiccant 18 movement between the adsorption zone and thedesorption zone, controlling a speed of blower 42 and/or circulator 46,and/or the like, based, on measurements of one or more of such inputs(e.g., such that controller 50 may optimize liquid water productionbased on current environmental and system conditions). As described inmore detail below, inputs to controller 50 may be measured in that theyare indicated in data captured by one or more sensors (e.g., 122).

Specific controller embodiments and functions are described in greaterdetail in the “Control Systems and Methods” section below. Controller 50is discussed in the “Water Extraction” section to explain how acontroller may be integrated into the system 10 in general. However, itwill be apparent to those of ordinary skill in the art that additionaland/or alternative functions (e.g., those described in the “ControlSystems and Methods” section) may be performed by controller 50 and/orother control systems in various water extraction system embodiments.

FIG. 2 is a diagram of an embodiment 98 of a system for generatingliquid water from air. System 98 may be substantially similar to system10, with the primary differences and/or additions described below.Otherwise, system 98 may comprise any and/or all features described withrespect to system 10.

In system 98, as with system 10, desiccant 18 (or a first portionthereof) may be in fluid communication with process air in process airpathway 26 while the desiccant 14 (or a second portion thereof) issimultaneously in fluid communication with regeneration fluid inregeneration fluid pathway 34, and, thus, desiccant unit 14 operates ina continuous and non-batch manner. In this embodiment, sections ofdesiccant 18 may be exposed to air in process air pathway 26 and fluidin regeneration fluid pathway 34 in an alternating manner.

System 98 may comprise a rotatable disk 102 (e.g., with desiccant 18disposed thereon). Desiccant 18 (or sections thereof) may be configuredto move between the adsorption zone and the desorption zone as disk 102is rotated. For example, in the depicted orientation of disk 102, aportion 106 of the desiccant is in communication with process airpathway 26, and a portion 110 of the disk is in communication withregeneration fluid pathway 34. System 98 may comprise an actuator (e.g.,electrical motor) 114 configured to cause rotation of disk 102.Controller 50 may be configured to optimize liquid water production atleast by controlling movement (e.g., through control of actuator 114) ofdesiccant 18 (e.g., disk 102) between the adsorption zone and thedesorption zone. In other embodiments, motor 114 may rotate disk 102 ata predetermined rotation rate.

System 98 may comprise a solar power unit 118 configured to providepower to at least a portion of system 98 (e.g., blower 42, circulator46, actuator 114, and/or the like). Solar power unit 118 may beconfigured to convert solar insolation to electrical power (e.g., solarpower unit 118 comprises a solar panel). For example, solar power unit118 may be provided as a photovoltaic solar panel comprisingsemiconducting materials exhibiting a photovoltaic effect. In these andsimilar embodiments, controller 50 may be configured to control system98 in response to diurnal variations in solar insolation (e.g., anamount of electrical power generated by solar power unit 118).

Systems for generating liquid water from air may be modular in nature.For example, systems may be configured such that each component (e.g.solar power unit 118, thermal unit 54, desiccant unit 14, condenser 80,water collection unit 84, and/or the like) may be separated from oneanother, transported, assembled and/or re-assembled with one another(e.g., in a same or a different configuration), and/or the like. Forexample, in some embodiments, the system may be configured such that nodimension of any singular component (e.g., water collection unit 84,desiccant unit 14, solar power unit 118, thermal unit 54, condenser 80,and/or the like) is larger than six to eight feet (e.g., to facilitatetransport of the system or components thereof, for example, in a singlecab truck bed, such as a bed of a Toyota Hilux pickup truck) (e.g., eachcomponent has a footprint that is less than or equal to 64 square feet(ft²) and/or each component can be contained within a cubic volume lessthan or equal to 512 cubic feet (ft³)).

Controller 50 may be configured to control one or more of blower 42,circulator 46, actuator 114, and/or the like (e.g., to optimize liquidwater production, where such control may be in response to diurnalvariations, for example, in ambient temperature, ambient air relativehumidity, solar insolation, and/or the like). For example, controller 50may be configured to increase a rate of liquid water production bycontrolling blower 42, circulator 46, actuator 114, and/or the like,taking into account, for example, diurnal variations. Such variationsmay change the amount of thermal energy generated by thermal unit 54,the level of electrical power provided by solar power unit 118, thelevel of humidity in process air entering the system, and/or the like.In some embodiments, ambient conditions may be measured in real-time orcan be forecast based on, for example, historical averages and/or thelike. In embodiments in which controller 50 receives real-timemeasurements, various sensors (described in more detail below) mayprovide data indicative of ambient conditions to controller 50 (e.g.,continuously, periodically, when requested by controller 50, and/or thelike).

Controller 50 may operate the system based on one or more of: a userselection, data received from one or more sensors, programmatic control,and/or by any other suitable bases. For example, controller 50 may beassociated with peripheral devices (including sensors) for sensing datainformation, data collection components for storing data information,and/or communication components for communicating data informationrelating to the operation of the system.

System 98 may comprise one or more peripheral devices, such as sensors122 (e.g., temperature sensors 122 a, humidity sensors 122 b, solarinsolation sensor 122 c, flow rate sensors 122 d, water level sensors122 e, and/or the like). In some embodiments, one or more sensors (e.g.,122) may provide data indicative of ambient air temperature, ambient airrelative humidity, solar insolation, process air temperature,regeneration fluid temperature, process air relative humidity,regeneration fluid relative humidity, process air flow rate,regeneration fluid flow rate, liquid water production rate, water usagerate, and/or the like.

One or more sensors 122 may be located remotely from other components ofthe system and may provide captured data to the other components of thesystem via a wired and/or wireless connection. For example, a town,village, city, and/or the like may include a plurality of the presentsystems, and one of the plurality of the present systems may providedata indicative of ambient environmental conditions (e.g., airtemperature, air relative humidity, a solar insolation level, and/or thelike) to another one of the plurality of the present systems. In thisway, in some embodiments, a single sensor 122 may be shared by multiplesystems. In some embodiments, data communicated to a controller (e.g.,50) by one or more peripheral devices (e.g., one or more sensors 122)may be stored in a data logging unit.

System 98 may comprise a telematics unit (e.g., a transmitter, receiver,transponder, transverter, repeater, transceiver, and/or the like,sometimes referred to herein as “transceiver 126”). For example, atransceiver 126 may be configured to communicate data to and/or from thesystem (e.g., controller 50) via a wired and/or wireless interface(e.g., which may conform to standardized communications protocols, suchas, for example, GSM, SMS components operating at relatively low rates(e.g., operating every few minutes), protocols that may begeographically specified, and/or the like).

Transceiver 126 may be associated with a server and a communicationsnetwork for communicating information between the server and thetransceiver (e.g., and thus the system and/or a controller 50 thereof).Two-way communication may be facilitated by a cellular tower in cellularrange of the system. In some embodiments, a database (e.g., which may beremote from the system) may be configured to store information receivedfrom the server over the communications network.

In embodiments with telematics capability, a network administrator ordevice owner may send a command to controller 50 to update or deletelook-up table data (described below) and/or a control algorithm. In thisway, data security may be maintained, for example, in the case that thesystem is stolen or otherwise lost.

Controller 50 may be configured to vary operation of system 98 at leastbased on real-time and/or forecast variations in ambient conditions. Forexample, controller 50 may control exposure of desiccant 18 (e.g., orsections thereof) to process air and regeneration fluid in response tochanges in ambient conditions (e.g., by changing the rotational speed ofdisk 102, such that the time that a portion of desiccant 18 disposedthereon is exposed to process air in process air pathway 26 orregeneration fluid in regeneration fluid pathway 34 may be increased ordecreased). In some embodiments, controller 50 may be configured to varya size of an adsorption zone or a desorption zone (e.g., in response todiurnal variations).

FIG. 3A is a graph of diurnal variations in environmental conditionsover one day, including ambient air relative humidity (“RH”) andtemperature. FIG. 3B is a graph of diurnal variations in environmentalconditions over one day, including solar radiation (e.g., solarinsolation). During nighttime hours, ambient air relative humidity maybe relatively high, and ambient temperature may be relatively low. Asthe sun rises, solar insolation may increase (e.g., peaking aroundnoon), which may result in a decrease in ambient air relative humidityand an increase in ambient temperature. At a certain point during theday, ambient air relative humidity may reach a minimum, and, at acertain point during the day, ambient temperature may increase to amaximum, and these points may generally coincide. Finally, as the sunbegins to set, ambient air relative humidity may tend to increase, andambient temperature may tend to decrease (e.g., as solar insolationapproaches its minimum during nighttime hours).

As shown, a particular set of environmental conditions may exist at eachpoint in a diurnal cycle (e.g., ambient air relative humidity, ambienttemperature, solar insolation, and/or the like). The system may beconfigured to vary operational parameters (e.g., control variables),taking into account variations in these environmental conditions, thusoptimizing system performance (e.g., liquid water production) for eachpoint of the diurnal cycle. By way of illustration, in the early part ofa day, solar insolation may be relatively limited. Thus, in someembodiments, the system (e.g., or a controller 50 thereof) may adjustoperational parameters to account for a relatively low amount ofavailable solar thermal energy and/or a relatively low amount ofelectrical power available from solar power units, despite the relativehigh ambient air relative humidity. For example, in these circumstances,a controller may cause a desiccant to move more slowly between anadsorption zone and a desorption zone due to the relatively low amountof thermal energy and/or solar power available, despite the relativelyhigh levels of ambient air relative humidity in available process air.On the other hand, later in the day, the controller may adjustoperational parameters to account for a relatively low amount of ambientair relative humidity, despite a relatively high amount of availablesolar thermal energy and/or a relatively high amount of electrical poweravailable from solar power units (e.g., due to a relatively high amountof solar insolation). Controllers may make such adjustments tooperational parameters periodically and/or continuously.

FIG. 4 is a diagram illustrating example flow paths through someembodiments of the present systems for generating liquid water from air.Embodiments of the present systems for generating liquid water from airmay comprise any suitable flow path (e.g., process air pathway and/orregeneration fluid pathway), including, for example, those describedbelow (e.g., whether alone and/or in combination), which are providedmerely by way of example.

In some embodiments, air within the process air pathway may enter thesystem from an outside environment, communicate with sections A, B, C,E, and F of a desiccant 18 (e.g., such that the desiccant or sectionsthereof may absorb water from the air in the process air pathway), passthrough a condenser 80 (e.g., where air in the process air pathway maybe heated by thermal energy from fluid in the regeneration fluidpathway), and be exhausted to the outside environment. In these andsimilar embodiments, regeneration fluid may pass through a condenser 80(e.g., where fluid in the regeneration fluid pathway may transferthermal energy to air in the process air pathway), pass through athermal unit 54 (e.g., where fluid in the regeneration fluid pathway maybe heated), communicate with section D of a desiccant 18 (e.g., suchthat the desiccant or sections thereof may release water to fluid in theregeneration fluid pathway), and flow back through the condenser (e.g.,such that the condenser may produce liquid water from fluid in theregeneration fluid pathway).

In some embodiments, the present systems may include a purge airflowpath 130 configured to transfer thermal energy from regeneration fluidin a regeneration fluid pathway downstream of a desiccant 18 to fluid inthe regeneration fluid pathway upstream of the condenser. For example,in these and similar embodiments, process air may enter the system froman outside environment, communicate with sections A, B, and F of adesiccant 18, pass through a condenser 80, and be exhausted to theoutside environment. In these and similar embodiments, regenerationfluid may pass through a condenser 80, pass through a thermal unit 54,communicate with section D of a desiccant 18, and flow back through thecondenser. In these and similar embodiments, air in a purge airflow path130 may communicate between section E of a desiccant 18 and section D ofthe desiccant (e.g., to transfer heat from section D of the desiccant,which may be provided to section D of the desiccant by regenerationfluid within the regeneration fluid pathway flowing from a thermal unit54 to section E of the desiccant) (e.g., to perform a pre-heatingoperation before section E of the desiccant moves into a desorptionzone).

Some embodiments may comprise a recovery heat exchanger 134 configuredto transfer thermal energy from regeneration fluid in a regenerationfluid pathway downstream of a desiccant 18 to fluid in the regenerationfluid pathway upstream of the condenser. For example, in these andsimilar embodiments, process air may enter the system from an outsideenvironment, communicate with sections A, B, C, E, and F of a desiccant18, pass through a condenser 80, and be exhausted to the outsideenvironment. In these and similar embodiments, regeneration fluid maypass through a condenser 80, pass through a heat exchanger (e.g., suchthat the heat exchanger may transfer thermal energy from fluid in theregeneration fluid pathway downstream of the desiccant to fluid in theregeneration fluid pathway upstream of the condenser), pass through athermal unit 54, communicate with section D of the desiccant, flow backthrough the heat exchanger, and flow back through the condenser. In thisway, thermal energy that may otherwise be lost to the environmentthrough the condenser may be at least partially recovered to be used fordesorption purposes.

Some embodiments may comprise a second desiccant 138 (e.g., which may bedisposed on a disk, similarly to as described above for desiccant 18)configured to transfer water from fluid in the regeneration fluidpathway downstream of a condenser 80 to fluid in the regeneration fluidpathway upstream of the condenser. For example, in these and similarembodiments, process air may enter the system from an outsideenvironment, communicate with sections A, B, C, E, and F of a desiccant18, pass through a condenser 80, and be exhausted to the outsideenvironment. In these and similar embodiments, regeneration fluid maypass through a condenser 80, communicate with section L of a seconddesiccant 138 (e.g., such that desiccant 138 may capture water in fluidin the regeneration fluid pathway before the fluid in the regenerationfluid pathway enters thermal unit 54), pass through a thermal unit 54,communicate with section D of the desiccant, communicate with section Kof the second desiccant (e.g., such that desiccant 138 may release waterto fluid in the regeneration fluid pathway before fluid in theregeneration fluid pathway enters condenser 80), and flow back throughthe condenser.

Some embodiments may achieve at least some of the functionalitydescribed above for a regeneration fluid pathway in communication with asecond desiccant 138 without requiring a second desiccant. For example,in some embodiments, process air may enter the system from an outsideenvironment, communicate with sections A, E, and F, of a desiccant 18,pass through a condenser 80, and be exhausted to the outsideenvironment. n these and similar embodiments, regeneration fluid maypass through a condenser 80, communicate with section C of a desiccant18, pass through a thermal unit 54, communicate with section D of thedesiccant, communicate with section B of the desiccant, and flow backthrough the condenser.

In some embodiments, process air may enter the system from an outsideenvironment, communicate with section A, E, and F of a desiccant 18,pass through a condenser 80, and be exhausted to an outside environment.In these and similar embodiments, regeneration fluid may pass through acondenser 80, communicate with section C of a desiccant 18, pass througha thermal unit 54, communicate with section D of the desiccant, and flowback through the condenser. Such embodiments may achieve at least someof the benefits of embodiments having a recovery heat exchanger 134 or apurge airflow path 130.

In some embodiments, process air may enter the system from an outsideenvironment, communicate with sections A, B, E, and F of a desiccant 18,pass through a condenser 80, and be exhausted to an outside environment.In these and similar embodiments, regeneration fluid may pass through acondenser 80, flow through a recovery heat exchanger 134, communicatewith section C of a desiccant 18, pass through a thermal unit 54,communicate with section D of the desiccant, flow back through therecovery heat exchanger, and flow back through the condenser.

In some embodiments of the present systems (e.g., 10, 98, and/or thelike), production rate of liquid water (H₂O_(rate)) may be expressed, atleast in part, as a function of environmental conditions (e.g., ambientair temperature (T_(amb)), ambient air relative humidity (RH_(amb)), andsolar insolation (Q_(solar))), as well as system operating parameters(e.g., control variables) (e.g., process air flow rate (V_(process)),regeneration fluid flow rate (V_(regen)), and exposure time of adesiccant to process air and regeneration fluid (e.g., which, for adesiccant disposed on a rotatable disk, may be a function of a rotationrate of the rotatable disk (ω_(disk)))) (Eq. 1).

H ₂ O _(rate) =f(T _(amb) ,RH _(amb) ,Q _(solar),ω_(disk) ,V _(process),V _(regen))  (1)

Efficiency of some embodiments of the present systems may be expressedin a variety of ways. The following examples are provided only by way ofillustration, and each of the following examples may be used alone or incombination with other expressions (whether or not explicitly disclosedbelow) to describe an efficiency of some embodiments of the presentsystems. For example, efficiency may be defined as:

$\begin{matrix}{\eta = {\Delta \; H_{{vap},{H_{2}O}}\frac{m_{{{liquid}\mspace{11mu} H_{2}O},{produced}}}{Q_{total}}}} & (2)\end{matrix}$

where η represents efficiency, ΔH_(vap,H) ₂ _(O) represents the heat ofvaporization of water, m_(liquid H) ₂ _(O,produced) represents a mass ofliquid water produced, and Q_(total) represents the heat energy requiredby the system to produce the mass of liquid water. From Eq. 2, it can beseen that an efficiency of 100% equates to 2260 joules (J) of heatenergy required to produce 1 gram (g) of liquid water.

In some embodiments, efficiency may be defined as regenerationefficiency, or, for example:

$\begin{matrix}{\eta = \frac{m_{{{liquid}\mspace{11mu} H_{2}O},{produced}}}{m_{{H_{2}O},{recirculating}}}} & (3)\end{matrix}$

where m_(H) ₂ _(O,recirculating) represents a total mass of waterpresent in the regeneration fluid pathway. As seen in Eq. 3, efficiencymay generally improve as exit temperature of regeneration fluid from thecondenser decreases.

In some embodiments, efficiency may be defined in terms of aneffectiveness parameter (e.g., determined from psychrometric charts).Such an effectiveness parameter may be defined, for example, as theratio of an actual amount of water adsorbed and/or desorbed by adesiccant to an idea isenthalpic path in the psychrometric chart. Toillustrate, an effectiveness parameter may tend towards a value of unity(one), with higher gel carrying capacities, decreased disk rotationrates, lower disk heat capacity, and/or the like.

In some embodiments, efficiency may be defined as dehumidificationeffectiveness, or, for example:

$\begin{matrix}{\eta = \frac{m_{{H_{2}O},{i\; n}} - m_{{H_{2}O},{out}}}{m_{{H_{2}O},{i\; n}}}} & (4)\end{matrix}$

where m_(H) ₂ _(O,in) represents a total mass of water present in airentering process air pathway 26, and m_(H) ₂ _(O,out) represents a totalmass of water leaving process air pathway 26.

As depicted in FIG. 5A, in some embodiments, a controller 50 may controlthe system operating parameters, based on one or more of theenvironmental conditions (e.g., which may be measured by and/orindicated in data captured by one or more sensors 122) in order tooptimize, for example, liquid water production. By way of illustration,in some embodiments, for each combination of particular environmentalconditions corresponding to a given point in the diurnal cycle (e.g., 0°C.<T_(amb)<45° C.; 20%<RH_(amb)<90%; 200 watts per square meter(W/m²)<Q_(solar)<1000 W/m²), the controller may perform a simulationusing a model of a system (e.g., 10, 98, and/or the like) to estimatethe optimal system operating parameters (e.g., (ω_(disk))_(optimum),(V_(process))_(optimum), and (V_(regen))_(optimum)), that maximizeand/or optimize liquid water production (e.g., as defined in Eq. 1),where:

(ω_(disk))_(optimum) =f(T _(amb) ,RH _(amb) ,Q _(solar))  (5)

(V _(process))_(optimum) =f(T _(amb) ,RH _(amb) ,Q _(solar))  (6)

(V _(regen))_(optimum) =f(T _(amb) ,RH _(amb) ,Q _(solar))  (7)

In some embodiments, a controller 50 may employ a control algorithm thatincorporates design variables (e.g. disk 102 geometry, such as, forexample, thickness, radius, and/or the like, thermal unit 54 geometry,and/or the like), and, in some embodiments, these design variables maybe incorporated in the control algorithm along with environmentalconditions (e.g. ambient air temperature, ambient air relative humidity,solar insolation, and/or the like).

As described above, in some embodiments, ambient air temperature andambient air relative humidity may be measured directly with one or moresensors 122. In some embodiments, solar insolation may be measuredindirectly (e.g., and continuously) by measuring a temperature of fluidin the regeneration fluid pathway between a thermal unit 54 and adesiccant 18 (e.g., at a known and controlled flow rate of regenerationfluid through the regeneration fluid pathway). In some embodiments, datacaptured by various sensor(s) may be transmitted to a controller (e.g.,which may be in communication with a memory that stores a look-up tablecontaining data generated during simulation runs) which then determinesthe optimum system operating parameters (e.g., process air flow rate,regeneration fluid flow rate, disk rotation rate, and/or the like).

In some embodiments, a numerical simulator may be used to create alook-up table of optimized operational parameters for the system. Forexample, in these embodiments, each run of the numerical simulator maytake a single set of design specifications (e.g. disk kinetics, disksize, desiccant configuration, solar collector size, condenser geometryand performance, and/or the like), instantaneous and/or forecast ambientconditions (e.g. ambient air temperature, ambient air relative humidity,a level of solar insolation), and system operation variables (e.g.,process air flow rate, regeneration fluid flow rate, desiccant exposuretime to process air and/or regeneration fluid, and/or the like) todetermine and/or estimate an optimized efficiency and/or liquid waterproduction rate for the system (e.g., which optimized values may varyover a diurnal cycle).

FIG. 5B is a flow chart of a non-limiting example of simulation-basedcontrol suitable for use in some embodiments of the present systems.Note that while simulation-based control may be used in some cases,additional control schemes and methods are discussed in the “ControlSystems and Methods” section below. As shown, the system may beinitialized at step 142 with one or more design inputs, control inputs,and/or controller variables. In this embodiment, design inputs caninclude one or more of system size, disk materials and/or dimensions,desiccant materials and/or dimensions, control inputs can includeambient air relative humidity (e.g., or a range thereof), ambient airtemperature (e.g., or a range thereof), and a level of solar insolation(e.g., or a range thereof), and controller variables may include processair flow rate, regeneration fluid flow rate, desiccant rate of movement,and/or the like. In some embodiments, one or more of the steps of thisexample may be performed by a controller 50. In some embodiments,certain steps depicted in FIG. 5B may be omitted.

At step 146, movement of a desiccant 18 may be simulated (e.g., bysimulating rotation of disk 102 by a small amount, such as, for example,from 1-5°). In this embodiment, at step 150, simulated process air maybe passed over a simulated condenser 80. In the depicted embodiment,also at step 150, process air temperature and process air relativehumidity may be recalculated (e.g., using thermodynamic equations) afterpicking up thermal energy within the simulated condenser. At step 154,in this embodiment, process air fluid communication with the desiccantmay be simulated, and process air temperature and process air relativehumidity may be recalculated based on the simulated interaction with thedesiccant.

At step 158, a simulation of regeneration fluid passing through athermal unit (e.g., 54) may be performed, where regeneration fluidtemperature and regeneration fluid relative humidity may be recalculated(e.g., again, using thermodynamic equations). In the depictedembodiment, at step 162, regeneration fluid communication with thedesiccant may be simulated, and the system may determine theregeneration fluid temperature and regeneration fluid relative humidityafter the simulated interaction with the desiccant. In this embodiment,also at step 162, the system may determine the temperature and watercontent of the desiccant (or a portion thereof). In some embodiments,temperature sensor may provide readings more quickly than humiditysensor. To compensate for this effect, controller 50 may synchronize thereadings by passing temperature readings through a signal filter (e.g.,a first-order low-pass digital filter implemented in controller 50hardware or software or firmware executed by controller 50) to slow thetemperature sensor reading response time to match the response time ofthe humidity sensor. At step 166, regeneration fluid passing through thecondenser may be simulated, and the regeneration fluid temperature andthe regeneration fluid relative humidity may be recalculated. As in step162, in some embodiments controller 50 may synchronize the readings bypassing temperature readings through a signal filter (e.g., afirst-order low-pass digital filter implemented in controller 50hardware or software or firmware executed by controller 50) to slow thetemperature sensor reading response time to match the response time ofthe humidity sensor. In some embodiments, the amount of condensed waterproduced may also be calculated at step 166. At step 170, the systems ofequations used to perform at least some of steps 146 through 166 may beevaluated to determine if a steady state solution has been reached. Inthis embodiment, if no steady state solution has been reached, the mainloop may be repeated beginning at step 146.

Once a steady state solution is reached, in the embodiment shown, thecontroller 50 may set the process air flow rate, the regeneration fluidflow rate, and the rate of movement of the desiccant (e.g., in a realsystem, for example, corresponding to the simulated system used toperform the steps of FIG. 5B) to optimize liquid water production and/orefficiency. The above steps are provided only by way of example, as, insome embodiments, the sequence of these steps may be changed. Forexample, in another embodiment, two separate process air pathways mayexist such that in one of the process air pathways, process air passesthrough a condenser 80, and in the other of the process air pathways,process air passes through a desiccant 18, and the above steps may bemodified accordingly.

In some embodiments, each run of the simulation depicted in FIG. 5B mayproduce a single data point in the data look-up table (e.g., liquidwater production rate and/or efficiency) as a function of the designinputs, control inputs, and/or control variables. Such a numericalsimulation may be repeated many times (e.g. from 100 to 100,000 times ormore) to produce a look-up table of liquid water production rates and/orefficiencies as a function of the relevant variables. Such a table maythen be used by a controller 50 to operate a system (e.g, 10, 98, and/orthe like), for example, by referencing optimal control variables (e.g.,process air flow rate, regeneration fluid flow rate, desiccant movementrate, and/or the like) based upon known design inputs and/or measuredcontrol inputs (e.g., ambient air temperature, ambient air relativehumidity, a level of solar insolation, and/or the like).

By way of example, Table 1, below, provides optimized operatingconditions (e.g., control variables) versus design inputs and controlinputs for an embodiment of the present systems that includes a disk 102having a silica desiccant disposed thereon.

TABLE 1 TABLE 1: Illustrative Optimal Operating Conditions and DesignSpecifications for an Embodiment of the Present Systems for GeneratingLiquid Water from Air Process Regeneration Liquid Ambient Desiccant AirFluid Disk Exhaust H₂0 Ambient Air Rotation Flow Flow Desiccant OuterProcess Production Air Temp Rate Rate Rate Heat Thickness Radius AirRate % RH (C) (°/s) (cfm) (cfm) (W) (m) (m) % RH (L/hr) Efficiency 20%10 0.6 90 4 300 0.05 0.12 9% 0.114789 24% 20% 10 1 90 4 400 0.05 0.12 7%0.128647 20% 20% 10 1.4 90 4 500 0.05 0.12 6% 0.126455 16% 20% 10 1 90 4600 0.05 0.12 6% 0.117378 12% 20% 10 1 90 4 700 0.05 0.12 6% 0.11732411% 20% 10 1 90 4 800 0.05 0.12 6% 0.117304 9% 20% 15 0.6 90 4 300 0.050.12 10% 0.116898 24% 20% 15 1 90 4 400 0.05 0.12 8% 0.135425 21% 20% 151.4 90 5 500 0.05 0.12 7% 0.13665 17% 20% 15 1.4 90 5 600 0.05 0.12 7%0.127931 13% 20% 15 1.4 90 4 700 0.05 0.12 7% 0.123528 11% 20% 15 1.4 904 800 0.05 0.12 7% 0.123402 10% 20% 20 0.6 90 4 300 0.05 0.12 11%0.114592 24% 20% 20 1 90 4 400 0.05 0.12 10% 0.136252 21% 20% 20 1.4 904 500 0.05 0.12 9% 0.140614 18% 20% 20 1.8 90 5 600 0.05 0.12 8%0.133403 14% 20% 20 1.4 90 4 700 0.05 0.12 8% 0.125402 11% 20% 20 1.8 906 800 0.05 0.12 7% 0.127496 10% 20% 25 1 90 4 300 0.05 0.12 12% 0.11752125% 20% 25 1 90 5 400 0.05 0.12 11% 0.142599 22% 20% 25 1.4 90 4 5000.05 0.12 9% 0.155649 20% 20% 25 1.8 90 5 600 0.05 0.12 8% 0.15298 16%20% 25 1.4 90 5 700 0.05 0.12 9% 0.151051 14% 20% 25 1.4 90 4 800 0.050.12 9% 0.137663 11% 20% 30 1 90 4 300 0.05 0.12 13% 0.120365 25% 20% 301.4 90 5 400 0.05 0.12 11% 0.144586 23% 20% 30 1.4 90 4 500 0.05 0.1210% 0.158795 20% 20% 30 1.4 90 4 600 0.05 0.12 10% 0.166699 17% 20% 301.8 90 5 700 0.05 0.12 9% 0.164122 15% 20% 30 2.6 90 6 800 0.05 0.12 8%0.148756 12% 20% 35 1 90 4 300 0.05 0.12 13% 0.117452 25% 20% 35 1.4 904 400 0.05 0.12 12% 0.139812 22% 20% 35 1.4 90 4 500 0.05 0.12 11%0.147449 19% 20% 35 1.4 90 4 600 0.05 0.12 11% 0.152162 16% 20% 35 1.490 4 700 0.05 0.12 11% 0.155368 14% 20% 35 1.4 90 4 800 0.05 0.12 11%0.157911 12% 30% 10 0.6 90 4 300 0.05 0.12 14% 0.129974 27% 30% 10 1 904 400 0.05 0.12 11% 0.15635 25% 30% 10 1 90 5 500 0.05 0.12 9% 0.16945521% 30% 10 1.4 90 5 600 0.05 0.12 8% 0.171671 18% 30% 10 1.4 90 5 7000.05 0.12 8% 0.169347 15% 30% 10 1.4 90 5 800 0.05 0.12 8% 0.169209 13%30% 15 0.6 90 4 300 0.05 0.12 16% 0.135576 28% 30% 15 1 90 4 400 0.050.12 13% 0.164791 26% 30% 15 1.4 90 5 500 0.05 0.12 11% 0.177866 22% 30%15 1.4 90 5 600 0.05 0.12 10% 0.181001 19% 30% 15 1.4 90 5 700 0.05 0.1210% 0.178858 16% 30% 15 1.4 90 5 800 0.05 0.12 10% 0.178663 14% 30% 200.6 90 4 300 0.05 0.12 17% 0.138859 29% 30% 20 1 90 4 400 0.05 0.12 14%0.170558 27% 30% 20 1.4 90 5 500 0.05 0.12 13% 0.186046 23% 30% 20 1.890 6 600 0.05 0.12 11% 0.190955 20% 30% 20 1.8 90 6 700 0.05 0.12 10%0.190329 17% 30% 20 1.8 90 6 800 0.05 0.12 10% 0.191953 15% 30% 25 0.690 4 300 0.05 0.12 18% 0.142598 30% 30% 25 1 90 4 400 0.05 0.12 16%0.181979 29% 30% 25 1.4 90 5 500 0.05 0.12 14% 0.205825 26% 30% 25 1.890 6 600 0.05 0.12 12% 0.217698 23% 30% 25 1.8 90 6 700 0.05 0.12 11%0.217838 20% 30% 25 2.2 90 6 800 0.05 0.12 11% 0.216324 17% 30% 30 0.690 4 300 0.05 0.12 19% 0.143171 30% 30% 30 1 90 4 400 0.05 0.12 17%0.188855 30% 30% 30 1.4 90 5 500 0.05 0.12 15% 0.215839 27% 30% 30 1.890 6 600 0.05 0.12 13% 0.228551 24% 30% 30 2.2 90 6 700 0.05 0.12 12%0.229472 21% 30% 30 2.2 90 6 800 0.05 0.12 12% 0.227413 18% 30% 35 0.690 5 300 0.05 0.12 21% 0.157775 33% 30% 35 1 90 4 400 0.05 0.12 18%0.190279 30% 30% 35 1.4 90 5 500 0.05 0.12 16% 0.216748 27% 30% 35 1.890 6 600 0.05 0.12 14% 0.256955 27% 30% 35 2.2 90 6 700 0.05 0.12 13%0.259982 23% 30% 35 2.6 90 7 800 0.05 0.12 12% 0.235721 18% 40% 10 0.690 4 300 0.05 0.12 19% 0.147654 31% 40% 10 0.6 90 4 400 0.05 0.12 16%0.182417 29% 40% 10 1 90 4 500 0.05 0.12 13% 0.209919 26% 40% 10 1.4 905 600 0.05 0.12 11% 0.218139 23% 40% 10 1.4 90 5 700 0.05 0.12 11%0.218186 20% 40% 10 1.4 90 5 800 0.05 0.12 11% 0.217967 17% 40% 15 0.690 4 300 0.05 0.12 21% 0.154558 32% 40% 15 1 90 4 400 0.05 0.12 18%0.189338 30% 40% 15 1 90 4 500 0.05 0.12 15% 0.219899 28% 40% 15 1.4 905 600 0.05 0.12 13% 0.230924 24% 40% 15 1.4 90 5 700 0.05 0.12 13%0.230829 21% 40% 15 1.4 90 5 800 0.05 0.12 13% 0.230595 18% 40% 20 0.690 4 300 0.05 0.12 23% 0.159779 33% 40% 20 1 90 4 400 0.05 0.12 20%0.197003 31% 40% 20 1 90 5 500 0.05 0.12 17% 0.228599 29% 40% 20 1.4 906 600 0.05 0.12 15% 0.247023 26% 40% 20 1.8 90 7 700 0.05 0.12 13%0.254703 23% 40% 20 1.8 90 6 800 0.05 0.12 13% 0.254027 20% 40% 25 0.690 4 300 0.05 0.12 25% 0.165997 35% 40% 25 1 90 4 400 0.05 0.12 21%0.209369 33% 40% 25 1 90 5 500 0.05 0.12 18% 0.247311 31% 40% 25 1.4 906 600 0.05 0.12 16% 0.275485 29% 40% 25 1.8 90 6 700 0.05 0.12 14%0.289535 26% 40% 25 2.2 90 7 800 0.05 0.12 13% 0.290837 23% 40% 30 0.690 4 300 0.05 0.12 26% 0.170385 36% 40% 30 1 90 4 400 0.05 0.12 22%0.218117 34% 40% 30 1.4 90 5 500 0.05 0.12 20% 0.255419 32% 40% 30 1.490 6 600 0.05 0.12 18% 0.288 30% 40% 30 1.8 90 6 700 0.05 0.12 16%0.305618 27% 40% 30 2.2 90 7 800 0.05 0.12 14% 0.306437 24% 40% 35 0.690 4 300 0.05 0.12 27% 0.170405 36% 40% 35 1 90 4 400 0.05 0.12 24%0.221043 35% 40% 35 1.4 90 5 500 0.05 0.12 21% 0.260556 33% 40% 35 1.890 6 600 0.05 0.12 19% 0.289696 30% 40% 35 1.8 90 6 700 0.05 0.12 17%0.307534 28% 40% 35 2.6 90 7 800 0.05 0.12 15% 0.30755 24% 50% 10 0.6 904 300 0.05 0.12 25% 0.161131 34% 50% 10 0.6 90 4 400 0.05 0.12 20%0.209095 33% 50% 10 1 90 4 500 0.05 0.12 16% 0.238543 30% 50% 10 1.4 905 600 0.05 0.12 14% 0.253661 27% 50% 10 1.4 90 6 700 0.05 0.12 12%0.260525 23% 50% 10 1.8 90 6 800 0.05 0.12 12% 0.258666 20% 50% 15 0.690 4 300 0.05 0.12 28% 0.168604 35% 50% 15 0.6 90 4 400 0.05 0.12 23%0.215671 34% 50% 15 1 90 4 500 0.05 0.12 19% 0.249856 31% 50% 15 1.4 905 600 0.05 0.12 17% 0.268291 28% 50% 15 1.4 90 6 700 0.05 0.12 15%0.276009 25% 50% 15 1.8 90 6 800 0.05 0.12 14% 0.276355 22% 50% 20 0.690 4 300 0.05 0.12 30% 0.174707 37% 50% 20 0.6 90 4 400 0.05 0.12 25%0.219977 35% 50% 20 1 90 5 500 0.05 0.12 22% 0.261604 33% 50% 20 1.4 906 600 0.05 0.12 19% 0.287784 30% 50% 20 1.8 90 7 700 0.05 0.12 17%0.305206 27% 50% 20 1.8 90 7 800 0.05 0.12 15% 0.314038 25% 50% 25 0.690 4 300 0.05 0.12 31% 0.182108 38% 50% 25 1 90 4 400 0.05 0.12 27%0.229061 36% 50% 25 1 90 5 500 0.05 0.12 23% 0.280957 35% 50% 25 1.4 906 600 0.05 0.12 20% 0.31591 33% 50% 25 1.8 90 7 700 0.05 0.12 18%0.340444 31% 50% 25 1.8 90 7 800 0.05 0.12 16% 0.355011 28% 50% 30 0.690 4 300 0.05 0.12 33% 0.188614 39% 50% 30 1 90 5 400 0.05 0.12 29%0.23885 37% 50% 30 1 90 5 500 0.05 0.12 25% 0.292067 37% 50% 30 1.4 90 6600 0.05 0.12 22% 0.331455 35% 50% 30 1.8 90 7 700 0.05 0.12 20%0.359095 32% 50% 30 2.2 90 7 800 0.05 0.12 18% 0.375297 29% 50% 35 0.690 4 300 0.05 0.12 34% 0.192377 40% 50% 35 1 90 5 400 0.05 0.12 30%0.244036 38% 50% 35 1 90 5 500 0.05 0.12 27% 0.295248 37% 50% 35 1.4 906 600 0.05 0.12 24% 0.338213 35% 50% 35 1.8 90 7 700 0.05 0.12 21%0.367278 33% 50% 35 2.2 90 7 800 0.05 0.12 19% 0.384249 30% 60% 10 0.690 5 300 0.05 0.12 31% 0.167431 35% 60% 10 0.6 90 4 400 0.05 0.12 25%0.227607 36% 60% 10 1 90 4 500 0.05 0.12 21% 0.259032 33% 60% 10 1 90 5600 0.05 0.12 17% 0.286405 30% 60% 10 1.4 90 6 700 0.05 0.12 15%0.298812 27% 60% 10 1.8 90 7 800 0.05 0.12 14% 0.298656 23% 60% 15 0.690 5 300 0.05 0.12 34% 0.17599 37% 60% 15 0.6 90 4 400 0.05 0.12 28%0.235977 37% 60% 15 1 90 5 500 0.05 0.12 24% 0.271262 34% 60% 15 1 90 5600 0.05 0.12 20% 0.300276 31% 60% 15 1.4 90 6 700 0.05 0.12 18%0.317478 28% 60% 15 1.8 90 7 800 0.05 0.12 16% 0.321377 25% 60% 20 0.690 4 300 0.05 0.12 36% 0.186651 39% 60% 20 0.6 90 4 400 0.05 0.12 30%0.243141 38% 60% 20 1 90 5 500 0.05 0.12 26% 0.284712 36% 60% 20 1 90 5600 0.05 0.12 23% 0.317663 33% 60% 20 1.4 90 7 700 0.05 0.12 20%0.347911 31% 60% 20 1.8 90 8 800 0.05 0.12 18% 0.365139 29% 60% 25 0.690 4 300 0.05 0.12 38% 0.194972 41% 60% 25 0.6 90 4 400 0.05 0.12 33%0.252843 40% 60% 25 1 90 5 500 0.05 0.12 28% 0.304025 38% 60% 25 1 90 5600 0.05 0.12 25% 0.344425 36% 60% 25 1.4 90 6 700 0.05 0.12 22%0.383939 34% 60% 25 1.8 90 7 800 0.05 0.12 19% 0.408065 32% 60% 30 0.690 4 300 0.05 0.12 39% 0.203487 43% 60% 30 0.6 90 4 400 0.05 0.12 34%0.259767 41% 60% 30 1 90 5 500 0.05 0.12 30% 0.31643 40% 60% 30 1.4 90 6600 0.05 0.12 27% 0.361017 38% 60% 30 1.4 90 6 700 0.05 0.12 24%0.402837 36% 60% 30 1.8 90 7 800 0.05 0.12 21% 0.430806 34% 60% 35 0.690 4 300 0.05 0.12 41% 0.210929 44% 60% 35 1 90 5 400 0.05 0.12 36%0.26243 41% 60% 35 1 90 6 500 0.05 0.12 32% 0.322488 40% 60% 35 1.4 90 6600 0.05 0.12 29% 0.370266 39% 60% 35 1.4 90 6 700 0.05 0.12 26%0.410392 37% 60% 35 1.8 90 7 800 0.05 0.12 23% 0.44132 35% 70% 10 0.6 905 300 0.05 0.12 37% 0.17757 37% 70% 10 0.6 90 5 400 0.05 0.12 30%0.237589 37% 70% 10 1 90 4 500 0.05 0.12 25% 0.275147 35% 70% 10 1 90 5600 0.05 0.12 21% 0.313577 33% 70% 10 1.4 90 6 700 0.05 0.12 18%0.330161 30% 70% 10 1.8 90 7 800 0.05 0.12 16% 0.335088 26% 70% 15 0.690 5 300 0.05 0.12 40% 0.186547 39% 70% 15 0.6 90 6 400 0.05 0.12 34%0.243351 38% 70% 15 1 90 5 500 0.05 0.12 28% 0.28831 36% 70% 15 1 90 5600 0.05 0.12 24% 0.328954 34% 70% 15 1.4 90 6 700 0.05 0.12 21%0.350796 31% 70% 15 1.8 90 7 800 0.05 0.12 19% 0.361302 28% 70% 20 0.690 4 400 0.05 0.12 36% 0.259806 41% 70% 20 1 90 5 500 0.05 0.12 31%0.302529 38% 70% 20 1 90 6 600 0.05 0.12 27% 0.347849 36% 70% 20 1.4 907 700 0.05 0.12 24% 0.382106 34% 70% 20 1.8 90 8 800 0.05 0.12 21%0.405931 32% 70% 25 0.6 90 5 300 0.05 0.12 45% 0.203098 43% 70% 25 0.690 4 400 0.05 0.12 38% 0.272149 43% 70% 25 1 90 6 500 0.05 0.12 34%0.322165 40% 70% 25 1 90 6 600 0.05 0.12 29% 0.374567 39% 70% 25 1.4 907 700 0.05 0.12 26% 0.416746 37% 70% 25 1.8 90 8 800 0.05 0.12 23%0.447221 35% 70% 30 0.6 90 5 300 0.05 0.12 46% 0.210718 44% 70% 30 0.690 4 400 0.05 0.12 40% 0.283104 44% 70% 30 1 90 6 500 0.05 0.12 36%0.335956 42% 70% 30 1 90 6 600 0.05 0.12 32% 0.389423 41% 70% 30 1.4 907 700 0.05 0.12 28% 0.436659 39% 70% 30 1.8 90 8 800 0.05 0.12 25%0.470857 37% 70% 35 0.6 90 5 300 0.05 0.12 48% 0.214885 45% 70% 35 0.690 4 400 0.05 0.12 42% 0.28812 45% 70% 35 1 90 6 500 0.05 0.12 38%0.343864 43% 70% 35 1 90 6 600 0.05 0.12 34% 0.395523 41% 70% 35 1.4 907 700 0.05 0.12 30% 0.447679 40% 70% 35 1.8 90 8 800 0.05 0.12 27%0.484405 38%

To illustrate how a controller 50 may rely on a look-up table to operatea system (e.g., 10, 98, and/or the like) a series of graphs is providedwith environmental conditions as independent variables, and efficiencyor liquid water production rate and system operating parameters as thedependent variables (e.g., and values illustrated in the below graphsmay be contained in a look-up table for reference by a controller).

For example, FIG. 6 is a graph illustrating an efficiency of someembodiments of the present systems for generating liquid water from air,at a constant process airflow rate of 90 (cfm), versus ambient airtemperature (° C.) (“T1”), ambient air relative humidity (“RH1”), andsolar insolation as indicated by heat (W) provided by a thermal unit,such that each point on the graph may represent a system efficiency at apoint in a diurnal cycle.

FIGS. 7A-7F show a series of graphs illustrating an efficiency of someembodiments of the present systems for generating liquid water from air(e.g., highest efficiency represented as darkest gray), at constantambient air relative humidities (“RH”), at a constant process airflowrate of 90 cfm, versus environmental diurnal variations, includingambient air temperature (° C.) and solar insolation as indicated by heat(W) provided by a thermal unit, such that each point on each graph mayrepresent a system efficiency at a point in a diurnal cycle.

FIGS. 8A-8F show a series of graphs illustrating a liquid waterproduction rate in kilograms per hour (kg/hr) of some embodiments of thepresent systems for generating liquid water from air (e.g., highestliquid water production rate represented as darkest gray), at constantambient air relative humidities (“RH”), at a constant process airflowrate of 90 cfm, versus environmental diurnal variations, includingambient air temperature (° C.) and solar insolation as indicated by heat(W) provided by a thermal unit, such that each point on each graph mayrepresent a system liquid water production rate at a point in a diurnalcycle (e.g., in Amman, Jordan, on a day in July, at 2:00 PM, RH was 26%(approximately 30%), and heat was 700 W (generated by a solar thermalunit having an area of 1.5 square meters (m2) at an efficiency of 50%),which resulted in a liquid water production rate of approximately 0.30kg/hr).

FIGS. 9A-9F show the series of graphs of FIG. 8, including pointsrepresenting various times on a given day. A total amount of liquidwater produced during the day may be approximated by integrating acrossthe series of graphs (e.g., in this example, approximately 2.5 liters(L) in the morning hours of the day, and approximately 5 L over a 24hour period).

In some embodiments, a controller 50 may reference a parametric functionand/or a table generated thereby to operate according to optimal (e.g.,in terms of liquid water production rate and/or efficiency) operationalvariables for the system. For example, for each system operationalvariable (e.g., process air flow rate, regeneration fluid flow rate,desiccant exposure time to process air and/or regeneration fluid, and/orthe like), a parametric function may be created that provides the valueof the system operational variable which optimizes efficiency and/orliquid water production rate of the system, and the parametric functionmay be dependent on design specifications (e.g., disk kinetics, disksize, desiccant configuration, solar collector size, condenser geometryand performance, and/or the like) and/or variable ambient conditions(e.g., ambient air temperature, ambient air relative humidity, a levelof solar insolation).

By way of illustration, an example derivation of a two variableparametric function is provided below. In this example, a simulation(e.g., as described above with respect to FIG. 5B) may be performedholding all variables constant except for a system operational variable(e.g., in the following example, ambient air temperature is heldconstant, and regeneration fluid flow rate may be varied). In subsequentsteps, the simulation may be repeated, changing the value of theconstant (e.g., ambient air temperature, in this example) betweensimulations in order to develop multiple data sets. Table 2 providesexample efficiency data obtained from such simulations (e.g., seven datasets are represented in Table 2, representing simulations performed atseven values of constant ambient air temperature).

TABLE 2 Exemplary Efficiency versus Regeneration Fluid Flow Rate Datafor an Embodiment of the Present Systems for Generating Liquid Waterfrom Air Temperature MFRi (° C.) (cfm) Efficiency 16 16 0.497785 16 180.491958 16 20 0.486554 16 22 0.480552 16 24 0.473718 16 26 0.465896 1628 0.457135 16 30 0.44745 16 32 0.436656 18 16 0.483841 18 18 0.47654618 20 0.47014 18 22 0.463751 18 24 0.457388 18 26 0.4503 18 28 0.44247318 30 0.433895 18 32 0.42459 20 16 0.472329 20 18 0.465762 20 200.459357 20 22 0.453557 20 24 0.447222 20 26 0.440308 20 28 0.43278 2030 0.424646 20 32 0.415998 22 16 0.463092 22 18 0.458915 22 20 0.4510522 22 0.446573 22 24 0.439184 22 26 0.432482 22 28 0.425249 22 300.417523 22 32 0.409271 24 16 0.45443 24 18 0.448595 24 20 0.443568 2422 0.438111 24 24 0.432175 24 26 0.425737 24 28 0.418852 24 30 0.41219524 32 0.403517 26 16 0.446432 26 18 0.441048 26 20 0.436394 26 220.431265 26 24 0.42722 26 26 0.419593 26 28 0.413006 26 30 0.405906 2632 0.398322 28 16 0.437145 28 18 0.433456 28 20 0.432251 28 22 0.42454728 24 0.419341 28 26 0.413667 28 28 0.407432 28 30 0.400671 28 320.393431 22 26 0.432482

Data from Table 2, above, is illustrated in FIG. 10. In this example, amathematical regression may be used to model each data set. Toillustrate, a polynomial (e.g., quadratic) regression may be fitted toeach data set using the following equations:

η=a ₁ V _(regen) ² +b ₁ V _(regen) +c ₁ at T _(amb,1)  (8)

η=a ₂ V _(regen) ² +b ₂ V _(regen) +c ₂ at T _(amb,2)  (9)

η=a _(n) V _(regen) ² +b _(n) V _(regen) +c _(n) at T _(amb,n)  (10)

where a, b, and, c, are coefficients of the quadratic regression foreach n data set. These coefficients may then modeled with a (e.g.,further) mathematical regression. To illustrate, in this example, aquadratic regression may be fitted to each set of coefficients, a, b,and c, using the following equations:

a=d ₁ T _(amb) ² +e ₁ T _(amb) +f ₁  (11)

b=d ₂ T _(amb) ² +e ₂ T _(amb) +f ₂  (12)

c=d ₃ T _(amb) ² +e ₃ T _(amb) +f ₃  (13)

FIGS. 11A and 11B provide graphs of these coefficients versus T_(amb).Through substitution, it may be seen that the efficiency of the systemas a function of T_(amb) and V_(regen) may then be expressed as:

η=(d ₁ T _(amb) ² +e ₁ T _(amb) +f ₁)V _(regen) ²(d ₂ T _(amb) ² +e ₂ T_(amb) +f ₂)V _(regen)+(d ₃ T _(amb) ² +e ₃ T _(amb) +f ₃)  (14)

While Eq. 14 is expressed in terms of two variables (e.g., V_(regen),and T_(amb)), the same or a substantially similar process as describedabove can be performed to express efficiency (e.g., and/or liquid waterproduction rate, and/or the like) as a function of any suitable numberof variables (e.g., by performing an additional regression for eachadded variable).

The maximum efficiency and/or maximum liquid water production rate(e.g., which may be the desired operational state for a system) may bedetermined by maximizing Eq. 14 (or a similar equation) with respect toeach operational variable (e.g., V_(regen), in this example). By way ofillustration, in the depicted example, the desired operational statethat maximizes efficiency may be the value of V_(regen) at which thepartial derivative of Eq. 14 with respect to V_(regen) at a given (e.g.,or measured) T_(amb) is equal to zero, or:

$\begin{matrix}{{\frac{\partial\eta}{\partial V_{regen}}}_{T_{amb}} = 0} & (15)\end{matrix}$

Eq. 15 (or similar equation(s)) may be evaluated over a range of ambientconditions, which may be used to produce a table of optimal operationalvariables (e.g., in this example, optimal V_(regen) for a range ofT_(amb)). Such tables may then be further modeled by a mathematicalregression (e.g., a quadratic regression). In this example, this may beshown as:

V _(regen,optimal) =gT _(amb) ² +hT _(amb)  (16)

where V_(regen,optimal) represents the optimal regeneration fluid flowrate at a given temperature. A controller 50 may then reference any of:the table of optimal operational variables, a parametric equation basedon the table of optimal operational variables (e.g., Eq. 16), and/or thelike. In some embodiments, a controller 50 may perform any and/or all ofthe above steps to develop such parametric equation(s) and/or tables. Insome embodiments, a controller 50 may be programmed with such parametricequations, for example, in some embodiments, the controller may beprogrammed with the following equations:

ω_(disk,optimal) =f(T _(amb) ,RH _(amb) ,T _(regen))  (17)

V _(process,optimal) =f(T _(amb) ,RH _(amb) ,T _(regen))  (18)

V _(regen,optimal) =f(T _(amb) ,RH _(amb) ,T _(regen))  (19)

where ω_(disk,optimal), V_(process,optimal), and V_(regen,optimal)represent optimal disk rotation rate, process air flow rate, andregeneration fluid flow rate operational variables at given values ofambient air temperature, ambient air relative humidity, and regenerationfluid temperature (e.g., indicative of a level of solar insolation).

Control Systems and Methods

FIG. 12 is a diagram of a system 1000 for generating liquid water fromair according to an embodiment of the invention. Similarly to system 10described above, system 1000 may be configured to function responsive todiurnal variations. For example, as described in more detail below,system 1000 may be configured to control one or more operationalparameters (e.g., control and/or controlled variables) based on one ormore diurnal variations (e.g., variations in ambient air temperature,ambient air relative humidity, solar insolation, and/or the like).

System 1000 may comprise a primary desiccant unit 1040 and secondarydesiccant unit 1045. Each desiccant unit 1040/1045 may comprise adesiccant (e.g., sorption medium), where the desiccant (e.g., or aportion thereof) may be selectively (e.g., and/or alternatively) movablebetween zones. The desiccant in the primary desiccant unit 1040 may bemovable between an adsorption zone, in which the desiccant is in fluidcommunication with a process air pathway (e.g., a process airflow path)1026 and a desorption zone, in which the desiccant is in fluidcommunication with a (e.g., closed-loop) regeneration fluid pathway(e.g., a regeneration fluid path) 1034. The desiccant in the secondarydesiccant unit 1045 may be movable between different sections of theregeneration fluid pathway 1034. In some embodiments, the adsorption anddesorption zones may be defined by housings of each desiccant unit1040/1045. Each desiccant unit 1040/1045 may be configured similarly tothose of system 10 above (e.g., the materials, desiccants used,arrangements, and/or operations may be as described above).

Similarly to system 10, system 1000 may include one or more blowersand/or one or more circulators. For example, a blower may be disposed inprocess air pathway 1026 and may be configured to adjust a flow rate ofair through the process air pathway. A circulator may be disposed inregeneration fluid pathway 1034 and may be configured to adjust a flowrate of fluid through the regeneration fluid pathway. In someembodiments, blowers and/or circulators may be controlled by controller1050 (e.g., controlling speeds of blowers and/or circulators to optimizeliquid water production). In some embodiments, blowers and/orcirculators may be configured to substantially maintain a pre-determinedflow rate through process air pathway 1026 and/or regeneration fluidpathway 1034.

System 1000 may comprise a thermal unit 1054 configured to providethermal energy to fluid in regeneration fluid pathway 1034 (e.g., suchthat desiccant may be regenerated). In some embodiments, thermal unit1054 may be a solar thermal unit (e.g., is configured to convert solarinsolation to thermal energy). While the present systems may compriseany suitable thermal unit, whether solar or otherwise, thermal unit 1054may be similar to thermal unit 54 described above, for example.

System 1000 may comprise a condenser 1080 configured to receive fluidfrom the desorption zone via the regeneration fluid pathway and produceliquid water from the received fluid (e.g., by condensing water vapor influid in the regeneration fluid pathway). Condenser 1080 may compriseany suitable material and may be of any suitable configuration. Forexample, condenser 1080 may be similar to condenser 80 described above.

System 1000 may comprise a water collection unit 1084 configured toreceive liquid water produced by condenser 1080. Water collection unit1084 may be similar to water collection unit 84 described above, forexample. In some embodiments, a filter may be positioned betweencondenser 1080 and water collection unit 1084 (e.g., to reduce an amountof impurities, such as, for example, sand, bacteria, fibrous,carbonaceous species, and/or the like, which may be present in liquidwater produced by condenser 1080). Water collection unit 1084 (e.g., orfilter thereof) may comprise an ultraviolet (UV) light source, one ormore water level sensors, and/or a receptacle configured to receive oneor more additives for introduction to the produced liquid water, such asthose described in the context of system 10 above.

System 1000 may comprise indicators (e.g., lights, such as, for example,LEDs), which may be configured to provide information regarding systemoperation. For example, indicators may be configured similarly to thosein system 10, as described above.

A controller (e.g., processor) 1050 may control exposure of desiccant(or a portion thereof) to air in process air pathway 1026 andregeneration fluid in regeneration fluid pathway 1034 (e.g., to increaseand/or optimize the liquid water ultimately produced by condenser 1080),and such control may vary over a diurnal cycle (e.g., in response todiurnal variations). Such variations in environmental conditions (e.g.,inputs into controller 1050) may include, for example, ambient airtemperature, ambient air relative humidity, and solar insolation. Otherinputs to controller 1050 may include, for example, an amount of thermalenergy generated by thermal unit 1054, a relative humidity of air inprocess air pathway 1026, a relative humidity of fluid in regenerationfluid pathway 1034, a temperature of fluid in the regeneration fluidpathway between desiccant and thermal unit 1054, a rate of waterproduction, and/or the like. Controller 1050 may be configured tooptimize liquid water production by controlling a rate of desiccantmovement between the adsorption zone and the desorption zone,controlling a speed of blower and/or circulator, and/or the like, based,on measurements of one or more of such inputs (e.g., such thatcontroller 1050 may optimize liquid water production based on currentenvironmental and system conditions). Controller may be powered byphotovoltaic power source (PV) 1090. Generally, controller 1050 mayperform functions similar to those detailed in the “Water Extraction”section.

FIG. 13 is a diagram of a controller 1050 according to an embodiment ofthe invention. Controller 1050 of FIG. 13 is one example embodimentwhich may be configured to perform the functions described herein,although those of ordinary skill in the art will appreciate that otherconfigurations may be possible. Controller 1050 may be powered by PV1090. Controller 1050 may include a microcontroller 1305, for example amicrocontroller based on the STM32F401—ARM Cortex-M4 with FPU.Controller 1050 may include a motor power supply 1310 (e.g., based on asynchronous buck topology) for powering motors such as those used todrive the desiccant wheels and/or fans. Controller 1050 may include adesiccant wheel motor controller power supply 1315 (e.g., based on abuck topology) for powering motor controllers. Controller 1050 mayinclude three motor/fan pulse width modulation (PWM) outputs 1320 andfive motor/fan tachometer inputs 1325 for controlling and monitoringmotors and fans. Controller 1050 may include three external NTCthermistor temperature inputs 1330, one on-board temperature andhumidity sensor 1335, one interface to an off-board temperature andhumidity sensor 1340, one water level input 1345, and one digital flowmeter input 1350 for receiving sensor data. Controller 1050 may includea LED driver for 3 ultraviolet LEDs 1355 and three drivers for statusLEDs 1360 for controlling the LEDs. Controller 1050 may include a UARTinterface to GSM or other radio transceiver 1365 for networkcommunications and a USB or other hardware interface 1370 (e.g., toenable communication with a PC-based service tool). Controller 1050 mayinclude serial EEPROM or other memory 1375.

Controller 1050 may be configured to control operations of system 1000through execution of instructions stored in memory 1375 bymicrocontroller 1305, for example. Controller 1050 may control system1000 operation through control of wheel motor operation and speed, regenfan operation and speed, and process fan operation and speed. Inembodiments wherein one or more of the sensors output analog signals,microcontroller 1305 may use an analog to digital converter to receivesensor outputs. For example, PV voltage, PV current, 12V voltage (e.g.,from one or more power supplies), wheel motor currents, fan currents,and/or LED currents may be sensed with sensors outputting analogsignals. Other sensors may output digital signals, and microcontroller1305 may read such signals directly. For example, humidity, temperature,water level, and water flow may be sensed with sensors outputtingdigital signals. Controller 1050 may control system 1000 to optimizewater production as described below. Additionally, controller 1050 maybe used with systems 10 and 98, for example, or other water collectionsystems, to control such systems to optimize water production in thosesystems in like fashion.

In some embodiments, sensors may not deliver outputs at similar speeds.For example, temperature sensor may provide readings more quickly thanhumidity sensor. In some embodiments, humidity sensor readings may lagbehind temperature sensor readings by 18 seconds. To compensate for thiseffect, controller 1050 may include a signal filter (e.g., a first-orderlow-pass digital filter implemented in controller 1050 hardware orsoftware or firmware executed by controller 1050). For example, for afilter having a time constant of 6 seconds (i.e., the time it takes thefiltered content to reach 63.2% of its step value), the filter may havea cut off frequency of 0.026526 Hz. Temperature sensor readings may passthrough the signal filter to slow the temperature sensor readingresponse time to match the response time of the humidity sensor.Accordingly, temperature sensor readings and humidity sensor readingsmay be synchronized when relative humidity is not at steady state.

Controller 1050 may determine motor and/or fan speed by measuring aperiod from rising edge to rising edge of each tachometer feedbacksignal and converting the measured period to RPM, given that there maybe two tachometer pulses per revolution. Controller 1050 may output aPWM signal for each motor/fan with a nominal frequency of 100 kHz, forexample. Speed control error may be reduced by performing PIDclosed-loop feedback speed control.

Water flow may be determined by controller 1050 through sensing ofrising and falling edges in the output of a digital water flow meter(e.g., where each edge represents 5 mL of water production).

Status LEDs 1360 may include a system on (e.g. green) LED, a maintenancerequired (e.g., yellow) LED, and/or a general failure (e.g., red) LED.Controller 1050 may communicate specific data through control of thestatus LEDs 1360. For example, controller 1050 may blink system on LEDat a rate of 1 Hz with 25% duty cycle whenever the system is powered on,thereby indicating normal operation. Controller 1050 may activate themaintenance required LED whenever the water filter life remaining fallsbelow 5%. Controller 1050 may operate the general failure LED in avariety of patterns to indicate different failures. For example, thefollowing patterns may be used in some embodiments:

1. regen fan failure—1 blink followed by 5 seconds of off time

2. wheel motor failure—2 blinks followed by 5 seconds of off time

3. process fan failure—3 blinks followed by 5 seconds of off time

wherein a blink may be defined as 0.25 seconds on followed by 0.25seconds off, for example. If multiple failure conditions are active,controller 1050 may control the general failure LED to blink through theactive patterns consecutively.

Controller 1050 may operate in a variety of modes. For example, bydefault in some embodiments, controller 1050 may operate in a run mode,wherein the microcontroller 1305 may execute autonomous tasks such asobtaining measurements from sensors, controlling motors and fans,controlling LEDs, optimizing water flow, optimizing water production,enabling a service interface (e.g., interface 1370), and/or gatheringand/or reporting telematics information (e.g., via transceiver 1365).

Controller 1050 may be operable in a full mode, for example whencontroller 1050 determines through sensor data that the water level inreservoir 1084 has reached a threshold level (e.g., reached a depth atwhich a maximum water level sensor is mounted). In full mode, controller1050 may turn off motors and fans (e.g., to halt accumulation ofmoisture in desiccants and flow of fluids) while continuing to operatethe service interface and telematics features.

Controller 1050 may be operable in a stop mode, for example whencontroller 1050 receives a stop command through interface 1370 ortransceiver 1365. In stop mode, controller 1050 may turn off motors andfans while continuing to operate the service interface and telematicsfeatures. When controller 1050 receives a start command throughinterface 1370 or transceiver 1365, controller 1050 may transition torun mode.

Controller 1050 may be operable in a test mode, for example whencontroller 1050 receives a test command through interface 1370 (e.g.,from a service tool or other computer coupled to interface 1370). Intest mode, controller 1050 may communicate input values from sensors tothe service tool and/or accept commands for controlling outputs from theservice tool. When controller 1050 receives a run command throughinterface 1370 or after a period of receiving no commands throughinterface 1370 (e.g., 5 seconds or some other period of time),controller 1050 may transition to run mode.

Controller 1050 may control the components of system 1000 to optimizewater production. For example, controller 1050 may control system 1000to refrain from producing water when environmental conditions are suchthat water cannot be produced (or cannot be produced at a desiredefficiency level), such as at night when solar thermal unit 1054 cannotoperate. At such times, controller 1050 may control system 1000 tooperate in a “no-go” mode. When water may be produced efficiently,controller 1050 may control system 1000 to produce the water (i.e., tooperate in a “go” mode).

FIG. 14 is a go/no-go mode determination process 1400 according to anembodiment of the invention. After a power-on reset, controller 1050 mayoperate in the no-go mode 1410. While in this mode, controller 1050 mayset the wheel motor speeds and regen fan speeds to speeds at or nearminimum operating levels (e.g., supplying minimum operating voltage sothat they may be quickly sped up when transitioning to go mode). Forexample, controller 1050 may set the wheel motor speeds to 125 RPM(assuming gear ratio of 3000:1, this may result in a wheel speed of 0.25degrees per second), and controller 1050 may set the set the regen fanto a speed of 2000 RPM, for example, which may result in an air flowrate of less than 10 CFM.

In some embodiments, controller 1050 may completely power off the wheelmotors and fans in no-go mode. In such cases, controller 1050 maymonitor PV power to formulate an estimate of the solar energy taken inby solar thermal unit 1054, for example. If PV 1090 is receiving solarenergy and using it to generate electricity, solar energy taken in bysolar thermal unit 1054 may be estimated based on how much electricityis being generated by PV 1090. When PV power reaches a specifiedthreshold, wheel motors and fans may be turned on in anticipation ofentering go mode shortly thereafter.

While in no-go mode, controller 1050 may calculate the dew point as afunction of ambient relative humidity and the hot-side temperatureaccording to Eq. 20 (or similar equation) 1420. Ambient relativehumidity and hot-side temperature may be obtained from a humidity sensorplaced on the outside of system 1000 and a temperature sensor placedbetween thermal unit 1054 and primary desiccant wheel 1040 or withinthermal unit 1054, respectively. As noted above, in some embodiments,temperature sensor output may pass through a filter to synchronize thetemperature sensor and humidity sensor outputs.

$\begin{matrix}{{DP} = \frac{243.04 \times \left\lbrack {{\ln \; {RH}} + \frac{17.625T}{243.04 + T}} \right\rbrack}{17.625 - {\ln \; {RH}} - \frac{17.625T}{243.04 + T}}} & (20)\end{matrix}$

Controller 1050 may transition to go mode if the calculated dew point isgreater than the ambient temperature plus some additional temperature(e.g., 10° C.). While in go mode, controller 1050 may maximize watercollection efficiency by maximizing VAP, which may be defined asabsolute humidity of the air between the primary and secondary desiccantwheels (estimated via Eq. 21 or similar or observed directly via asensor disposed in regeneration fluid pathway 1034 between the primarydesiccant wheel 1040 and secondary desiccant wheel 1045) multiplied byregeneration fluid flow (Eq. 22 or similar).

$\begin{matrix}{{AH} = \frac{6.112 \times e^{\lbrack\frac{17.67 \times T}{T + 243.5}\rbrack} \times {RH} \times 2.1674}{273.15 + T}} & (21) \\{{VAP} = {{Flow}_{Regen} \times {AH}}} & (22)\end{matrix}$

When go mode is entered, fan and wheel speeds may be adjusted tostarting values and subsequently modified to maximize VAP. In someembodiments, starting values may be defaults (e.g., fan speed set suchthat regeneration fluid flow is approximately 30 CFM, desiccant wheelspeed set to 0.25° of rotation per second). In some embodiments,starting values may be established dynamically. For example, startingvalues may be based upon previously established optimal values forsimilar conditions obtained at system 1000 or from another system incommunication with system 1000. Starting values may be prescribed by auser (e.g., via network or service tool). Starting values may be basedon a prediction made according to the efficiency models described abovein the “Water Extraction” section. Starting values may be based on aprevious day's values at time start+X (e.g., where X=1 hour or someother time that may allow VAP to be maximized), which may be stored inmemory 1375.

Periodically (e.g., after a certain amount of time, such as 30 secondsin one example, elapses) 1440, controller 1050 may perturb regen fanspeed 1450 to maximize VAP. For example, controller 1050 may make aninitial VAP determination and adjust regen fan speed upward (faster) ordownward (slower). If adjusting the fan speed upward causes VAP toincrease, controller 1050 may adjust fan speed upward again in the nextperiod. If adjusting the fan speed upward causes VAP to decrease,controller 1050 may adjust fan speed downward in the next period.Likewise, if adjusting the fan speed downward causes VAP to increase,controller 1050 may adjust fan speed downward again in the next period.If adjusting the fan speed downward causes VAP to decrease, controller1050 may adjust fan speed upward in the next period.

Similarly, controller 1050 may periodically (e.g., after a certainamount of time, such as 300 seconds in one example, elapses) 1460perturb desiccant wheel speed 1470 to maximize VAP. Controller 1050 mayperturb desiccant wheel speed less frequently than regen fan speed insome embodiments (e.g., once for every ten perturbations of regen fanspeed). For example, controller 1050 may make an initial VAPdetermination and adjust desiccant wheel speed upward (faster) ordownward (slower). If adjusting the desiccant wheel speed upward causesVAP to increase, controller 1050 may adjust desiccant wheel speed upwardagain in the next period. If adjusting the desiccant wheel speed upwardcauses VAP to decrease, controller 1050 may adjust desiccant wheel speeddownward in the next period. Likewise, if adjusting the desiccant wheelspeed downward causes VAP to increase, controller 1050 may adjustdesiccant wheel speed downward again in the next period. If adjustingthe desiccant wheel speed downward causes VAP to decrease, controller1050 may adjust desiccant wheel speed upward in the next period.

While operating in go mode, controller 1050 may continue to calculateEq. 20 periodically to track the relationship between dew point andambient temperature 1480. If the calculated dew point falls below theambient temperature plus some additional temperature (e.g., 5° C.),controller 1050 may switch back to no-go mode, as it may no longer beefficient or possible to produce water in such conditions.

When VAP is maximized, perturbations of fan speed and wheel speed maytend to cause fan speed and wheel speed to oscillate closely about theoptimal settings for maximizing VAP. Such settings may be observed bycontroller 1050 and stored in memory 1375 along with observed operatingconditions (e.g., Eq. 20, ambient humidity, etc.). Accordingly, thestored observations may be used to define starting settings on future gomode startups as noted above. When transitioning to go mode, controller1050 may compare current conditions with previously observed settings atsimilar conditions and set initial fan speed and wheel speed valuesaccording to the stored settings.

Controller 1050 may control primary wheel 1040 and secondary wheel 1045to operate at the same speed and at the same time. For example, in someembodiments secondary wheel 1045 may be controlled with the same controlsignal as primary wheel 1040. However, in other embodiments, controller1050 may perform active control of secondary wheel 1045. Active controlof secondary wheel 1045 may be undertaken to further optimize watervapor exchange from condenser 1080 outlet to condenser 1080 inlet andfurther optimize the transfer of heat from the inlet side to the outletside of condenser 1080.

Active control of secondary wheel 1045 may be managed in a variety ofways. For example, one or more sensors may be installed at the inlet tocondenser 1080 (i.e., the outlet of secondary wheel 1045) to monitorrelative humidity and temperature. Under the assumption that relativehumidity at the outlet to condenser 1080 may be 100%, and given that theexpected condenser efficiency, flow characteristics, and other designvariables may be known, the temperature at the outlet to condenser 1080may be implicitly known. To optimize this temperature, controller 1050may modulate secondary wheel 1045 speed to maximize absolute humidity atthe inlet to condenser 1080. Similar to 1460-1480 of FIG. 14, controller1050 may wait for a period of time to elapse and perturb the speed ofsecondary wheel 1405. After changing the speed, controller 1050 maymonitor sensors at the inlet to condenser 1080 to see if absolutehumidity has increased or decreased. If absolute humidity has increased,on the next cycle controller 1050 may perturb speed of secondary wheel1405 in the same direction as last time. If absolute humidity hasdecreased, on the next cycle controller 1050 may perturb speed ofsecondary wheel 1405 in the opposite direction as last time. In anotherexample, relative humidity alone may be monitored at the inlet tocondenser 1080 and maximized through the same perturbation technique.

Note that in embodiments wherein a relative humidity and temperaturesensor are disposed at an inlet of condenser 1080, VAP may be calculateddifferently. Assuming 100% relative humidity at condenser 1080 output,and measuring temperature at condenser 1080 output via a temperaturesensor, may yield the following:

VAP=  (23)

In some embodiments, relative humidity may also be monitored at theoutlet of condenser 1080. It may be possible to meet the go conditionand see less than 100% relative humidity on the outlet of condenser1080. This may indicate that system 100 has not crossed through the dewpoint in the condenser 1080, suggesting a potential problem at somepoint in the system 100 (e.g., a control error or leak).

Controller 1050 may also perform maximum power point tracking (MPPT) ofPV 1090. For example, controller 1050 may track MPPT by perturbingprocess fans according to Table 2: MPPT Truth Table. Changes in PVvoltage and power may be observed as a result of fan speed adjustment,and fans may be perturbed periodically to maximize PV output (with theunderstanding that PV output may necessarily be affected by regen fanand motor speed, which may be assumed as givens for the purposes ofMPPT).

TABLE 2 MPPT Truth Table PV Power PV Voltage Action Decrease DecreaseDecrease process fan speed Decrease Increase Increase process fan speedYes No Increase process fan speed Yes Yes Decrease process fan speed

FIG. 16 is a diagram of an MPPT approach 1600 according to an embodimentof the invention. The primary electrical loads during the day mayinclude a set of high-powered fans 1610 and 1620 (e.g., regen fan andprocess fan). Controller 1050 may include closed-loop speed controllersfor fans 1610 and 1620. Controller 1050 may use respective tachometerfeedback signals from each fan 1610 and 1620 to measure fan speed.Controller 1050 may use respective PWM signals to set fan speeds foreach fan 1610 and 1620. Controller 1050 may perturb the fan speeds bychanging the PWM duty cycle and observe the power delivered by PV 1090using a voltage measurement and a current sensor, thus resulting inMPPT.

Using transceiver 1365, system 1000 may join a network of similarsystems and other devices. FIG. 15 is a network 1500 of water generatingsystems 1000 according to an embodiment of the invention. Individualsystems 1000A-E may be able to communicate with one another usingtransceiver 1365, which may be, for example, a GSM radio or an 802.15.4radio. Each controller 1305 may include a network protocol stack (e.g.,MiWi, 6LoWPAN, etc.) for creating a wireless mesh network 1500connecting one or more systems 1000A-D to a remote gateway 1510. Fivesystems 1000A-E and one gateway 1510 are shown in this example, althoughany number of systems and/or gateways may be possible. In some cases,gateway 1510 may be integrated into one or more of systems 1000.

In some embodiments, systems 1000 may communicate with one another, suchthat one system 1000 may forward communications for another system 1000to and from gateway 1510 (e.g., as shown in FIG. 15, where systems A andC communicate with system D, and system B communicates with system C)and/or may communicate directly with gateway 1510 (e.g., systems D andE). Gateway 1510 may be connected to another network (e.g., theInternet) via any suitable networking hardware (e.g., cellular datamodem, wired or wireless Internet connection, etc.). Accordingly,systems 1000 may communicate, via the Internet through gateway 1510,with remote servers.

Each system 1000 may gather telemetry data and report it to a server vianetwork 1500. For example, controller 1050 may periodically (e.g., everytwo minutes) assemble and send a data stream including some or all ofthe following data elements to a configured e-mail address using SMS orsome other suitable protocol if a GSM radio is connected, or to a remotegateway 1510: ambient temperature, hot-side temperature, ambientrelative humidity, external relative humidity, PV voltage, PV current,PV power, wheel motor target speed, wheel motor measured speed, regenfan target speed, regen fan measured speed, process fan target speed,process fan measured speed, VAP, and/or accumulated water count.Controller 1050 may also receive commands via network 1500, for example,but not limited to start water production, stop water production, readconfiguration, write configuration, and/or reboot. Controller 1050 mayalso accept memory programming commands for upgrades. Controller 1050may make use of AES-128 encryption or other suitable security measuresto transfer memory programming data and CRC algorithms to ensure memoryprogramming data integrity in some embodiments.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example and notlimitation. It will be apparent to persons skilled in the relevant artsthat various changes in form and detail can be made therein withoutdeparting from the spirit and scope. In fact, after reading the abovedescription, it will be apparent to one skilled in the relevant arts howto implement alternative embodiments. In addition, it should beunderstood that any figures that highlight the functionality andadvantages are presented for example purposes only. The disclosedmethodology and system are each sufficiently flexible and configurablesuch that they may be utilized in ways other than that shown.

Although the term “at least one” may often be used in the specification,claims and drawings, the terms “a”, “an”, “the”, “said”, etc. alsosignify “at least one” or “the at least one” in the specification,claims, and drawings.

Finally, it is the applicant's intent that only claims that include theexpress language “means for” or “step for” be interpreted under 35U.S.C. 112(f). Claims that do not expressly include the phrase “meansfor” or “step for” are not to be interpreted under 35 U.S.C. 112(f).

1. A controller for controlling a system for extracting liquid water from air, the system comprising a thermal unit, a primary desiccant wheel, and a regeneration fluid path, the controller comprising: a plurality of sensors; a plurality of motors; and a microcontroller coupled to the plurality of sensors and the plurality of motors, the microcontroller being configured to: determine a water extraction efficiency based on at least one signal received from at least one of the plurality of sensors; and maximize the water extraction efficiency by adjusting a speed of at least one of the plurality of motors in response to the determined water extraction efficiency; wherein the water extraction efficiency is a value obtained by multiplying a regeneration fluid flow rate within the regeneration fluid path by an absolute humidity of air on a side of the primary desiccant wheel opposite a side in communication with the thermal unit.
 2. The controller of claim 1, wherein at least one of the sensors comprises a flow sensor disposed in the regeneration fluid path.
 3. The controller of claim 2, wherein the at least one signal comprises a regeneration fluid flow rate signal from the flow sensor.
 4. The controller of claim 1, wherein at least one of the sensors comprises a humidity sensor disposed in the regeneration fluid path on the side of the primary desiccant wheel opposite a side in communication with the thermal unit.
 5. The controller of claim 4, wherein the at least one signal comprises a humidity signal from the humidity sensor.
 6. The controller of claim 1, wherein: at least one of the sensors comprises a humidity sensor disposed outside the system; and at least another one of the sensors comprises a temperature sensor disposed in or near the thermal unit.
 7. The controller of claim 6, wherein: the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; and the microcontroller is further configured to estimate the absolute humidity using the humidity signal and the temperature signal.
 8. The controller of claim 6, wherein: the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; and the microcontroller is further configured to determine a dew point using the humidity signal and the temperature signal.
 9. The controller of claim 6, wherein: the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; and the controller further comprises a filter configured to synchronize the temperature signal with the humidity signal.
 10. The controller of claim 1, wherein: the system further comprises a condenser including an inlet and an outlet; at least one of the sensors comprises a humidity sensor disposed at the inlet of the condenser; at least one of the sensors comprises a first temperature sensor disposed at the inlet of the condenser; and at least one of the sensors comprises a second temperature sensor disposed at the outlet of the condenser.
 11. The controller of claim 10, wherein the at least one signal comprises a humidity signal from the humidity sensor, a first temperature signal from the first temperature sensor, and a second temperature signal from the second temperature sensor.
 12. The controller of claim 1, wherein the microcontroller is further configured to selectively operate in: a go mode wherein the microcontroller controls the plurality of motors to cause the system to extract the water; and a no-go mode wherein the microcontroller controls the plurality of motors to prevent the system from extracting the water.
 13. The controller of claim 12, wherein the microcontroller is further configured to transition from the no-go mode to the go mode in response to determining that a dew point is above a threshold value based on the at least one signal received from the at least one of the plurality of sensors.
 14. The controller of claim 13, wherein: at least one of the sensors comprises a humidity sensor disposed outside the system; and at least another one of the sensors comprises a temperature sensor disposed in or near the thermal unit; the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; and the microcontroller is further configured to determine the dew point using the humidity signal and the temperature signal.
 15. The controller of claim 12, wherein the microcontroller is further configured to transition from the go mode to the no-go mode in response to determining that a dew point is below a threshold value based on the at least one signal received from the at least one of the plurality of sensors.
 16. The controller of claim 15, wherein: at least one of the sensors comprises a humidity sensor disposed outside the system; and at least another one of the sensors comprises a temperature sensor disposed in or near the thermal unit; the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; and the microcontroller is further configured to determine the dew point using the humidity signal and the temperature signal.
 17. The controller of claim 12, wherein the microcontroller is further configured to set at least one starting speed for at least one of the plurality of motors when transitioning from the no-go mode to the go mode.
 18. The controller of claim 17, further comprising a memory coupled to the microcontroller, wherein the at least one starting speed is based on at least one value stored in the memory corresponding to at least one speed known to maximize the water extraction efficiency for a condition detected by at least one of the plurality of sensors.
 19. The controller of claim 17, wherein: the at least one of the plurality of motors comprises a motor for driving the primary desiccant wheel, a motor for driving a fan in the regeneration fluid path, or a combination thereof; and the at least one starting speed comprises a rotation speed for the primary desiccant wheel, a flow rate for fluid in the regeneration fluid path, or a combination thereof.
 20. The controller of claim 1, wherein adjusting the speed comprises: increasing the speed in response to detecting an increase in the water generation efficiency; or decreasing the speed in response to detecting a decrease in the water generation efficiency.
 21. The controller of claim 20, wherein the at least one of the plurality of motors comprises a motor for driving the primary desiccant wheel, a motor for driving a fan in the regeneration fluid path, or a combination thereof.
 22. The controller of claim 20, further comprising a memory coupled to the microcontroller, wherein the microcontroller is further configured to store a log comprising the speed, the at least one signal, the water extraction efficiency, or a combination thereof in the memory.
 23. The controller of claim 1, further comprising a transceiver coupled to the microcontroller, wherein the microcontroller is configured to: send data comprising the speed, the at least one signal, the water extraction efficiency, or a combination thereof via the transceiver; receive command data, update data, or a combination thereof via the transceiver; or a combination thereof.
 24. The controller of claim 1, wherein the at least one signal comprises a signal indicative of ambient temperature, hot-side temperature, ambient relative humidity, external relative humidity, PV voltage, PV current, PV power, wheel motor target speed, wheel motor measured speed, regen fan target speed, regen fan measured speed, process fan target speed, process fan measured speed, water extraction efficiency, and/or accumulated water count, or a combination thereof.
 25. The controller of claim 1, wherein: the plurality of sensors comprises at least one PV output sensor; the plurality of motors comprises at least one process fan motor; and the microcontroller is configured to optimize PV output by adjusting a speed of the at least one process fan motor.
 26. The controller of claim 1, wherein the system further comprises a condenser and a secondary desiccant wheel disposed between the primary desiccant wheel and the compressor.
 27. The controller of claim 26, wherein the microcontroller is configured to optimize a humidity at an inlet of the condenser by adjusting a speed of the secondary desiccant wheel.
 28. A method for controlling a system for extracting liquid water from air, the system comprising a thermal unit, a primary desiccant wheel, and a regeneration fluid path, the method comprising: determining, with a microcontroller coupled to a plurality of sensors and a plurality of motors, a water extraction efficiency based on at least one signal received from at least one of the plurality of sensors; and maximizing, with the microcontroller, the water extraction efficiency by adjusting a speed of at least one of the plurality of motors in response to the determined water extraction efficiency; wherein the water extraction efficiency is a value obtained by multiplying a regeneration fluid flow rate within the regeneration fluid path by an absolute humidity of air on a side of the primary desiccant wheel opposite a side in communication with the thermal unit.
 29. The method of claim 28, wherein at least one of the sensors comprises a flow sensor disposed in the regeneration fluid path.
 30. The method of claim 29, wherein the at least one signal comprises a regeneration fluid flow rate signal from the flow sensor.
 31. The method of claim 28, wherein at least one of the sensors comprises a humidity sensor disposed in the regeneration fluid path on the side of the primary desiccant wheel opposite a side in communication with the thermal unit.
 32. The method of claim 31, wherein the at least one signal comprises a humidity signal from the humidity sensor.
 33. The method of claim 28, wherein: at least one of the sensors comprises a humidity sensor disposed outside the system; and at least another one of the sensors comprises a temperature sensor disposed in or near the thermal unit.
 34. The method of claim 33, wherein the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor, the method further comprising estimating, with the microcontroller, the absolute humidity using the humidity signal and the temperature signal.
 35. The method of claim 33, wherein the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor, the method further comprising determining, with the microcontroller, a dew point using the humidity signal and the temperature signal.
 36. The method of claim 33, wherein the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor, the method further comprising filtering the temperature signal to synchronize the temperature signal with the humidity signal.
 37. The method of claim 28, wherein: the system further comprises a condenser including an inlet and an outlet; at least one of the sensors comprises a humidity sensor disposed at the inlet of the condenser; at least one of the sensors comprises a first temperature sensor disposed at the inlet of the condenser; and at least one of the sensors comprises a second temperature sensor disposed at the outlet of the condenser.
 38. The method of claim 37, wherein the at least one signal comprises a humidity signal from the humidity sensor, a first temperature signal from the first temperature sensor, and a second temperature signal from the second temperature sensor.
 39. The method of claim 28, further comprising selectively operating the microcontroller in: a go mode wherein the microcontroller controls the plurality of motors to cause the system to extract the water; and a no-go mode wherein the microcontroller controls the plurality of motors to prevent the system from extracting the water.
 40. The method of claim 39, further comprising transitioning, with the microcontroller, from the no-go mode to the go mode in response to determining that a dew point is above a threshold value based on the at least one signal received from the at least one of the plurality of sensors.
 41. The method of claim 40, wherein: at least one of the sensors comprises a humidity sensor disposed outside the system; and at least another one of the sensors comprises a temperature sensor disposed in or near the thermal unit; and the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; the method further comprising determining, with the microcontroller, the dew point using the humidity signal and the temperature signal.
 42. The method of claim 39, further comprising transitioning, with the microcontroller, from the go mode to the no-go mode in response to determining that a dew point is below a threshold value based on the at least one signal received from the at least one of the plurality of sensors.
 43. The method of claim 42, wherein: at least one of the sensors comprises a humidity sensor disposed outside the system; and at least another one of the sensors comprises a temperature sensor disposed in or near the thermal unit; and the at least one signal comprises a humidity signal from the humidity sensor and a temperature signal from the temperature sensor; the method further comprising determining, with the microcontroller, the dew point using the humidity signal and the temperature signal.
 44. The method of claim 39, further comprising setting, with the microcontroller, at least one starting speed for at least one of the plurality of motors when transitioning from the no-go mode to the go mode.
 45. The method of claim 44, wherein the at least one starting speed is based on at least one value stored in a memory coupled to the microcontroller corresponding to at least one speed known to maximize the water extraction efficiency for a condition detected by at least one of the plurality of sensors.
 46. The method of claim 44, wherein: the at least one of the plurality of motors comprises a motor for driving the primary desiccant wheel, a motor for driving a fan in the regeneration fluid path, or a combination thereof; and the at least one starting speed comprises a rotation speed for the primary desiccant wheel, a flow rate for fluid in the regeneration fluid path, or a combination thereof.
 47. The method of claim 28, wherein adjusting the speed comprises: increasing the speed in response to detecting an increase in the water generation efficiency; or decreasing the speed in response to detecting a decrease in the water generation efficiency.
 48. The method of claim 47, wherein the at least one of the plurality of motors comprises a motor for driving the primary desiccant wheel, a motor for driving a fan in the regeneration fluid path, or a combination thereof.
 49. The method of claim 47, further comprising storing, with the microcontroller, a log comprising the speed, the at least one signal, the water extraction efficiency, or a combination thereof in a memory coupled to the microcontroller.
 50. The method of claim 28, further comprising: sending, with the microcontroller, data comprising the speed, the at least one signal, the water extraction efficiency, or a combination thereof via a transceiver coupled to the microcontroller; receiving, with the microcontroller, command data, update data, or a combination thereof via the transceiver; or a combination thereof.
 51. The method of claim 28, wherein the at least one signal comprises a signal indicative of ambient temperature, hot-side temperature, ambient relative humidity, external relative humidity, PV voltage, PV current, PV power, wheel motor target speed, wheel motor measured speed, regen fan target speed, regen fan measured speed, process fan target speed, process fan measured speed, water extraction efficiency, and/or accumulated water count, or a combination thereof.
 52. The method of claim 28, wherein: the plurality of sensors comprises at least one PV output sensor; and the plurality of motors comprises at least one process fan motor; the method further comprising optimizing, with the microcontroller, PV output by adjusting a speed of the at least one process fan motor.
 53. The method of claim 28, wherein the system further comprises a condenser and a secondary desiccant wheel disposed between the primary desiccant wheel and the compressor.
 54. The method of claim 53, further comprising optimizing, with the microcontroller, a humidity at an inlet of the condenser by adjusting a speed of the secondary desiccant wheel. 